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Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
.\" Copyright (c) 2001-2015 Mark R V Murray. All rights reserved.
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
random.4: Include description of knobs added in r346358 Reported by: ngie Sponsored by: Dell EMC Isilon
2019-04-19 17:15:58 +00:00
.Dd April 19, 2019
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Dt RANDOM 4
.Os
.Sh NAME
.Nm random
.Nd the entropy device
Add a SYNOPSIS section for io(4), mem(4), or random(4), since they are now optional devices. MFC after: 1 week
2004-10-03 13:14:20 +00:00
.Sh SYNOPSIS
Add DEV_RANDOM pseudo-option and use it to "include out" random(4) if desired. Retire randomdev_none.c and introduce random_infra.c for resident infrastructure. Completely stub out random(4) calls in the "without DEV_RANDOM" case. Add RANDOM_LOADABLE option to allow loadable Yarrow/Fortuna/LocallyWritten algorithm. Add a skeleton "other" algorithm framework for folks to add their own processing code. NIST, anyone? Retire the RANDOM_DUMMY option. Build modules for Yarrow, Fortuna and "other". Use atomics for the live entropy rate-tracking. Convert ints to bools for the 'seeded' logic. Move _write() function from the algorithm-specific areas to randomdev.c Get rid of reseed() function - it is unused. Tidy up the opt_*.h includes. Update documentation for random(4) modules. Fix test program (reviewers, please leave this). Differential Revision: https://reviews.freebsd.org/D3354 Reviewed by: wblock,delphij,jmg,bjk Approved by: so (/dev/random blanket)
2015-08-17 07:36:12 +00:00
.Cd "options RANDOM_LOADABLE"
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
.Cd "options RANDOM_ENABLE_ETHER"
Make the UMA harvesting go away completely if not wanted. Default to "not wanted". Provide and document the RANDOM_ENABLE_UMA option. Change RANDOM_FAST to RANDOM_UMA to clarify the harvesting. Remove RANDOM_DEBUG option, replace with SDT probes. These will be of use to folks measuring the harvesting effect when deciding whether to use RANDOM_ENABLE_UMA. Requested by: scottl and others. Approved by: so (/dev/random blanket) Differential Revision: https://reviews.freebsd.org/D3197
2015-08-22 12:59:05 +00:00
.Cd "options RANDOM_ENABLE_UMA"
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Sh DESCRIPTION
The
.Nm
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
device returns an endless supply of random bytes when read.
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Pp
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
The generator will start in an
Fix up the man page for random(4). This mainly removes no-longer-relevant details about HW RNGs, reseeding explicitly and user-supplied entropy.
2013-10-06 13:01:42 +00:00
.Em unseeded
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
state, and will block reads until it is seeded for the first time.
Fix up the man page for random(4). This mainly removes no-longer-relevant details about HW RNGs, reseeding explicitly and user-supplied entropy.
2013-10-06 13:01:42 +00:00
.Pp
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
To provide prompt access to the random device at boot time,
.Fx
Minor language improvements. Note that they can't be changed by sysctl (I think they can be changed as a tuneable.)
2021-07-29 08:23:39 +00:00
automatically saves some entropy data in
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
.Pa /boot/entropy
Minor language improvements. Note that they can't be changed by sysctl (I think they can be changed as a tuneable.)
2021-07-29 08:23:39 +00:00
for the
.Xr loader 8
to provide to the kernel.
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
Additional entropy is regularly saved in
.Pa /var/db/entropy .
This saved entropy is sufficient to unblock the random device on devices with
writeable media.
.Pp
Embedded applications without writable media must determine their own scheme
for re-seeding the random device on boot, or accept that the device
will remain unseeded and block reads indefinitely.
See
.Sx SECURITY CONSIDERATIONS
for more detail.
.Pp
In addition to
.Xr read 2 ,
the direct output of the abstract kernel entropy device can be read with
.Xr getrandom 2 ,
.Xr getentropy 3 ,
or the
.Xr sysctl 8
pseudo-variable
.Va kern.arandom .
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Pp
Fix a couple of typos. PR: docs/75410 Submitted by: "Paul A.Hoadley" <paulh@logicsquad.net> MFC after: 3 days
2004-12-23 00:27:03 +00:00
To see the current settings of the software
.Nm
device, use the command line:
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Pp
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
.Dl "sysctl kern.random"
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Pp
Cosmetic and spelling fixes. Includes some MDOC policework. Submitted by: ru (mostly)
2001-02-19 20:08:01 +00:00
which results in something like:
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Bd -literal -offset indent
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
kern.random.block_seeded_status: 0
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
kern.random.fortuna.minpoolsize: 64
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
kern.random.harvest.mask_symbolic: ENABLEDSOURCE,[DISABLEDSOURCE],...,CACHED
kern.random.harvest.mask_bin: 00000010000000111011111
kern.random.harvest.mask: 66015
kern.random.use_chacha20_cipher: 0
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
kern.random.random_sources: 'Intel Secure Key RNG'
random.4: Include description of knobs added in r346358 Reported by: ngie Sponsored by: Dell EMC Isilon
2019-04-19 17:15:58 +00:00
kern.random.initial_seeding.bypass_before_seeding: 1
kern.random.initial_seeding.read_random_bypassed_before_seeding: 0
kern.random.initial_seeding.arc4random_bypassed_before_seeding: 0
kern.random.initial_seeding.disable_bypass_warnings: 0
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Ed
Assorted markup, spelling, and grammar fixes.
2004-06-16 08:33:57 +00:00
.Pp
* Add random_adaptors.[ch] which is basically a store of random_adaptor's. random_adaptor is basically an adapter that plugs in to random(4). random_adaptor can only be plugged in to random(4) very early in bootup. Unplugging random_adaptor from random(4) is not supported, and is probably a bad idea anyway, due to potential loss of entropy pools. We currently have 3 random_adaptors: + yarrow + rdrand (ivy.c) + nehemeiah * Remove platform dependent logic from probe.c, and move it into corresponding registration routines of each random_adaptor provider. probe.c doesn't do anything other than picking a specific random_adaptor from a list of registered ones. * If the kernel doesn't have any random_adaptor adapters present then the creation of /dev/random is postponed until next random_adaptor is kldload'ed. * Fix randomdev_soft.c to refer to its own random_adaptor, instead of a system wide one. Submitted by: arthurmesh@gmail.com, obrien Obtained from: Juniper Networks Reviewed by: so (des)
2013-08-09 15:31:50 +00:00
Other than
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
.Va kern.random.block_seeded_status ,
.Va kern.random.fortuna.minpoolsize ,
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
and
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
.Va kern.random.harvest.mask ,
Minor language improvements. Note that they can't be changed by sysctl (I think they can be changed as a tuneable.)
2021-07-29 08:23:39 +00:00
all settings are read-only via
.Xr sysctl 8 .
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Pp
The
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
.Pa kern.random.fortuna.minpoolsize
sysctl is used
Spelling fixes supplied by pfg@, detected with codespell, plus additional misspellings detected by igor. MFC after: 1 week
2016-05-01 22:00:41 +00:00
to set the seed threshold.
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
A smaller number gives a faster seed,
but a less secure one.
In practice,
values between 64 and 256
are acceptable.
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
.Pp
The
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
.Va kern.random.harvest.mask
bitmask is used to select
the possible entropy sources.
A 0 (zero) value means
the corresponding source
is not considered
Document the entropy device. If you want to know how to harvest network traffic and interrupts, READ HERE!
2001-02-18 18:08:43 +00:00
as an entropy source.
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
Set the bit to 1 (one)
if you wish to use
that source.
- Bring kern.random output closer to reality - Remove kern.random.sys.burst, it's no longer available - Document kern.random.sys.harvest.swi (1) PR: 100167 (1) MFC after: 3 days
2006-07-19 10:49:43 +00:00
The
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
.Va kern.random.harvest.mask_bin
and
.Va kern.random.harvest.mask_symbolic
Add DEV_RANDOM pseudo-option and use it to "include out" random(4) if desired. Retire randomdev_none.c and introduce random_infra.c for resident infrastructure. Completely stub out random(4) calls in the "without DEV_RANDOM" case. Add RANDOM_LOADABLE option to allow loadable Yarrow/Fortuna/LocallyWritten algorithm. Add a skeleton "other" algorithm framework for folks to add their own processing code. NIST, anyone? Retire the RANDOM_DUMMY option. Build modules for Yarrow, Fortuna and "other". Use atomics for the live entropy rate-tracking. Convert ints to bools for the 'seeded' logic. Move _write() function from the algorithm-specific areas to randomdev.c Get rid of reseed() function - it is unused. Tidy up the opt_*.h includes. Update documentation for random(4) modules. Fix test program (reviewers, please leave this). Differential Revision: https://reviews.freebsd.org/D3354 Reviewed by: wblock,delphij,jmg,bjk Approved by: so (/dev/random blanket)
2015-08-17 07:36:12 +00:00
sysctls
can be used to confirm
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
settings in a human readable form.
Disabled items
Minor language improvements. Note that they can't be changed by sysctl (I think they can be changed as a tuneable.)
2021-07-29 08:23:39 +00:00
in the latter
Huge cleanup of random(4) code. * GENERAL - Update copyright. - Make kernel options for RANDOM_YARROW and RANDOM_DUMMY. Set neither to ON, which means we want Fortuna - If there is no 'device random' in the kernel, there will be NO random(4) device in the kernel, and the KERN_ARND sysctl will return nothing. With RANDOM_DUMMY there will be a random(4) that always blocks. - Repair kern.arandom (KERN_ARND sysctl). The old version went through arc4random(9) and was a bit weird. - Adjust arc4random stirring a bit - the existing code looks a little suspect. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Redo read_random(9) so as to duplicate random(4)'s read internals. This makes it a first-class citizen rather than a hack. - Move stuff out of locked regions when it does not need to be there. - Trim RANDOM_DEBUG printfs. Some are excess to requirement, some behind boot verbose. - Use SYSINIT to sequence the startup. - Fix init/deinit sysctl stuff. - Make relevant sysctls also tunables. - Add different harvesting "styles" to allow for different requirements (direct, queue, fast). - Add harvesting of FFS atime events. This needs to be checked for weighing down the FS code. - Add harvesting of slab allocator events. This needs to be checked for weighing down the allocator code. - Fix the random(9) manpage. - Loadable modules are not present for now. These will be re-engineered when the dust settles. - Use macros for locks. - Fix comments. * src/share/man/... - Update the man pages. * src/etc/... - The startup/shutdown work is done in D2924. * src/UPDATING - Add UPDATING announcement. * src/sys/dev/random/build.sh - Add copyright. - Add libz for unit tests. * src/sys/dev/random/dummy.c - Remove; no longer needed. Functionality incorporated into randomdev.*. * live_entropy_sources.c live_entropy_sources.h - Remove; content moved. - move content to randomdev.[ch] and optimise. * src/sys/dev/random/random_adaptors.c src/sys/dev/random/random_adaptors.h - Remove; plugability is no longer used. Compile-time algorithm selection is the way to go. * src/sys/dev/random/random_harvestq.c src/sys/dev/random/random_harvestq.h - Add early (re)boot-time randomness caching. * src/sys/dev/random/randomdev_soft.c src/sys/dev/random/randomdev_soft.h - Remove; no longer needed. * src/sys/dev/random/uint128.h - Provide a fake uint128_t; if a real one ever arrived, we can use that instead. All that is needed here is N=0, N++, N==0, and some localised trickery is used to manufacture a 128-bit 0ULLL. * src/sys/dev/random/unit_test.c src/sys/dev/random/unit_test.h - Improve unit tests; previously the testing human needed clairvoyance; now the test will do a basic check of compressibility. Clairvoyant talent is still a good idea. - This is still a long way off a proper unit test. * src/sys/dev/random/fortuna.c src/sys/dev/random/fortuna.h - Improve messy union to just uint128_t. - Remove unneeded 'static struct fortuna_start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) * src/sys/dev/random/yarrow.c src/sys/dev/random/yarrow.h - Improve messy union to just uint128_t. - Remove unneeded 'staic struct start_cache'. - Tighten up up arithmetic. - Provide a method to allow eternal junk to be introduced; harden it against blatant by compress/hashing. - Assert that locks are held correctly. - Fix the nasty pre- and post-read overloading by providing explictit functions to do these tasks. - Turn into self-sufficient module (no longer requires randomdev_soft.[ch]) - Fix some magic numbers elsewhere used as FAST and SLOW. Differential Revision: https://reviews.freebsd.org/D2025 Reviewed by: vsevolod,delphij,rwatson,trasz,jmg Approved by: so (delphij)
2015-06-30 17:00:45 +00:00
are listed in square brackets.
See
.Xr random_harvest 9
for more on the harvesting of entropy.
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
.Sh FILES
.Bl -tag -width ".Pa /dev/urandom"
.It Pa /dev/random
.It Pa /dev/urandom
.El
random.4: Include description of knobs added in r346358 Reported by: ngie Sponsored by: Dell EMC Isilon
2019-04-19 17:15:58 +00:00
.Sh DIAGNOSTICS
The following tunables are related to initial seeding of the
.Nm
device:
.Bl -tag -width 4
.It Va kern.random.initial_seeding.bypass_before_seeding
Defaults to 1 (on).
When set, the system will bypass the
.Nm
device prior to initial seeding.
On is
.Em unsafe ,
but provides availability on many systems that lack early sources
of entropy, or cannot load
.Pa /boot/entropy
sufficiently early in boot for
.Nm
consumers.
When unset (0), the system will block
.Xr read_random 9
and
.Xr arc4random 9
requests if and until the
.Nm
device is initially seeded.
.It Va kern.random.initial_seeding.disable_bypass_warnings
Defaults to 0 (off).
When set non-zero, disables warnings in dmesg when the
.Nm
device is bypassed.
.El
.Pp
The following read-only
.Xr sysctl 8
variables allow programmatic diagnostic of whether
.Nm
device bypass occurred during boot.
If they are set (non-zero), the specific functional unit bypassed the strong
.Nm
device output and either produced no output
.Xr ( read_random 9 )
or seeded itself with minimal, non-cryptographic entropy
.Xr ( arc4random 9 ) .
.Bl -bullet
.It
.Va kern.random.initial_seeding.read_random_bypassed_before_seeding
.It
.Va kern.random.initial_seeding.arc4random_bypassed_before_seeding
.El
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
.Sh SEE ALSO
.Xr getrandom 2 ,
.Xr arc4random 3 ,
.Xr getentropy 3 ,
.Xr random 3 ,
.Xr sysctl 8 ,
.Xr random 9
.Rs
.%A Ferguson
.%A Schneier
.%A Kohno
.%B Cryptography Engineering
.%I Wiley
.%O ISBN 978-0-470-47424-2
.Re
.Sh HISTORY
A
.Nm
device appeared in
.Fx 2.2 .
The implementation was changed to the
.Em Yarrow algorithm in
.Fx 5.0 .
In
.Fx 11.0 ,
the Fortuna algorithm was introduced as the default.
In
.Fx 12.0 ,
Yarrow was removed entirely.
.Sh AUTHORS
.An -nosplit
The current
.Nm
code was authored by
.An Mark R V Murray ,
with significant contributions from many people.
Add DEV_RANDOM pseudo-option and use it to "include out" random(4) if desired. Retire randomdev_none.c and introduce random_infra.c for resident infrastructure. Completely stub out random(4) calls in the "without DEV_RANDOM" case. Add RANDOM_LOADABLE option to allow loadable Yarrow/Fortuna/LocallyWritten algorithm. Add a skeleton "other" algorithm framework for folks to add their own processing code. NIST, anyone? Retire the RANDOM_DUMMY option. Build modules for Yarrow, Fortuna and "other". Use atomics for the live entropy rate-tracking. Convert ints to bools for the 'seeded' logic. Move _write() function from the algorithm-specific areas to randomdev.c Get rid of reseed() function - it is unused. Tidy up the opt_*.h includes. Update documentation for random(4) modules. Fix test program (reviewers, please leave this). Differential Revision: https://reviews.freebsd.org/D3354 Reviewed by: wblock,delphij,jmg,bjk Approved by: so (/dev/random blanket)
2015-08-17 07:36:12 +00:00
.Pp
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
The
.Em Fortuna
algorithm was designed by
.An Niels Ferguson ,
.An Bruce Schneier ,
and
.An Tadayoshi Kohno .
.Sh CAVEATS
Add DEV_RANDOM pseudo-option and use it to "include out" random(4) if desired. Retire randomdev_none.c and introduce random_infra.c for resident infrastructure. Completely stub out random(4) calls in the "without DEV_RANDOM" case. Add RANDOM_LOADABLE option to allow loadable Yarrow/Fortuna/LocallyWritten algorithm. Add a skeleton "other" algorithm framework for folks to add their own processing code. NIST, anyone? Retire the RANDOM_DUMMY option. Build modules for Yarrow, Fortuna and "other". Use atomics for the live entropy rate-tracking. Convert ints to bools for the 'seeded' logic. Move _write() function from the algorithm-specific areas to randomdev.c Get rid of reseed() function - it is unused. Tidy up the opt_*.h includes. Update documentation for random(4) modules. Fix test program (reviewers, please leave this). Differential Revision: https://reviews.freebsd.org/D3354 Reviewed by: wblock,delphij,jmg,bjk Approved by: so (/dev/random blanket)
2015-08-17 07:36:12 +00:00
When
.Cd "options RANDOM_LOADABLE"
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
is enabled,
Add DEV_RANDOM pseudo-option and use it to "include out" random(4) if desired. Retire randomdev_none.c and introduce random_infra.c for resident infrastructure. Completely stub out random(4) calls in the "without DEV_RANDOM" case. Add RANDOM_LOADABLE option to allow loadable Yarrow/Fortuna/LocallyWritten algorithm. Add a skeleton "other" algorithm framework for folks to add their own processing code. NIST, anyone? Retire the RANDOM_DUMMY option. Build modules for Yarrow, Fortuna and "other". Use atomics for the live entropy rate-tracking. Convert ints to bools for the 'seeded' logic. Move _write() function from the algorithm-specific areas to randomdev.c Get rid of reseed() function - it is unused. Tidy up the opt_*.h includes. Update documentation for random(4) modules. Fix test program (reviewers, please leave this). Differential Revision: https://reviews.freebsd.org/D3354 Reviewed by: wblock,delphij,jmg,bjk Approved by: so (/dev/random blanket)
2015-08-17 07:36:12 +00:00
the
.Pa /dev/random
device is not created
until an "algorithm module"
is loaded.
Remove the Yarrow PRNG algorithm option in accordance with due notice given in random(4). This includes updating of the relevant man pages, and no-longer-used harvesting parameters. Ensure that the pseudo-unit-test still does something useful, now also with the "other" algorithm instead of Yarrow. PR: 230870 Reviewed by: cem Approved by: so(delphij,gtetlow) Approved by: re(marius) Differential Revision: https://reviews.freebsd.org/D16898
2018-08-26 12:51:46 +00:00
The only module built by default is
.Em random_fortuna .
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
Loadable random modules
are less efficient
than their compiled-in equivalents.
Add DEV_RANDOM pseudo-option and use it to "include out" random(4) if desired. Retire randomdev_none.c and introduce random_infra.c for resident infrastructure. Completely stub out random(4) calls in the "without DEV_RANDOM" case. Add RANDOM_LOADABLE option to allow loadable Yarrow/Fortuna/LocallyWritten algorithm. Add a skeleton "other" algorithm framework for folks to add their own processing code. NIST, anyone? Retire the RANDOM_DUMMY option. Build modules for Yarrow, Fortuna and "other". Use atomics for the live entropy rate-tracking. Convert ints to bools for the 'seeded' logic. Move _write() function from the algorithm-specific areas to randomdev.c Get rid of reseed() function - it is unused. Tidy up the opt_*.h includes. Update documentation for random(4) modules. Fix test program (reviewers, please leave this). Differential Revision: https://reviews.freebsd.org/D3354 Reviewed by: wblock,delphij,jmg,bjk Approved by: so (/dev/random blanket)
2015-08-17 07:36:12 +00:00
This is because some functions
must be locked against
load and unload events,
and also must be indirect calls
to allow for removal.
Make the UMA harvesting go away completely if not wanted. Default to "not wanted". Provide and document the RANDOM_ENABLE_UMA option. Change RANDOM_FAST to RANDOM_UMA to clarify the harvesting. Remove RANDOM_DEBUG option, replace with SDT probes. These will be of use to folks measuring the harvesting effect when deciding whether to use RANDOM_ENABLE_UMA. Requested by: scottl and others. Approved by: so (/dev/random blanket) Differential Revision: https://reviews.freebsd.org/D3197
2015-08-22 12:59:05 +00:00
.Pp
When
.Cd "options RANDOM_ENABLE_UMA"
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
is enabled,
Make the UMA harvesting go away completely if not wanted. Default to "not wanted". Provide and document the RANDOM_ENABLE_UMA option. Change RANDOM_FAST to RANDOM_UMA to clarify the harvesting. Remove RANDOM_DEBUG option, replace with SDT probes. These will be of use to folks measuring the harvesting effect when deciding whether to use RANDOM_ENABLE_UMA. Requested by: scottl and others. Approved by: so (/dev/random blanket) Differential Revision: https://reviews.freebsd.org/D3197
2015-08-22 12:59:05 +00:00
the
.Pa /dev/random
device will obtain entropy
from the zone allocator.
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
This is a very high rate source with significant performance impact.
Therefore, it is disabled by default.
Add a section on different types of randomness, what the library functions we provide are good for and how /dev/random fits into this picture. Reviewed by: markm
2003-02-23 16:28:58 +00:00
.Pp
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
When
.Cd "options RANDOM_ENABLE_ETHER"
is enabled, the
A few improvements suggested by nectar.
2003-02-23 17:22:20 +00:00
.Nm
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
device will obtain entropy from
.Vt mbuf
structures passing through the network stack.
This source is both extremely expensive and a poor source of entropy, so it is
disabled by default.
.Sh SECURITY CONSIDERATIONS
The initial seeding
of random number generators
is a bootstrapping problem
that needs very careful attention.
When writable media is available, the
.Em Fortuna
paper describes a robust system for rapidly reseeding the device.
Add a section on different types of randomness, what the library functions we provide are good for and how /dev/random fits into this picture. Reviewed by: markm
2003-02-23 16:28:58 +00:00
.Pp
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
In some embedded cases, it may be difficult to find enough randomness to seed a
random number generator until a system is fully operational.
In these cases, is the responsibility of the system architect to ensure that
blocking is acceptable, or that the random device is seeded.
(This advice does not apply to typical consumer systems.)
Add a section on different types of randomness, what the library functions we provide are good for and how /dev/random fits into this picture. Reviewed by: markm
2003-02-23 16:28:58 +00:00
.Pp
random(4): Block read_random(9) on initial seeding read_random() is/was used, mostly without error checking, in a lot of very sensitive places in the kernel -- including seeding the widely used arc4random(9). Most uses, especially arc4random(9), should block until the device is seeded rather than proceeding with a bogus or empty seed. I did not spy any obvious kernel consumers where blocking would be inappropriate (in the sense that lack of entropy would be ok -- I did not investigate locking angle thoroughly). In many instances, arc4random_buf(9) or that family of APIs would be more appropriate anyway; that work was done in r345865. A minor cleanup was made to the implementation of the READ_RANDOM function: instead of using a variable-length array on the stack to temporarily store all full random blocks sufficient to satisfy the requested 'len', only store a single block on the stack. This has some benefit in terms of reducing stack usage, reducing memcpy overhead and reducing devrandom output leakage via the stack. Additionally, the stack block is now safely zeroed if it was used. One caveat of this change is that the kern.arandom sysctl no longer returns zero bytes immediately if the random device is not seeded. This means that FreeBSD-specific userspace applications which attempted to handle an unseeded random device may be broken by this change. If such behavior is needed, it can be replaced by the more portable getrandom(2) GRND_NONBLOCK option. On any typical FreeBSD system, entropy is persisted on read/write media and used to seed the random device very early in boot, and blocking is never a problem. This change primarily impacts the behavior of /dev/random on embedded systems with read-only media that do not configure "nodevice random". We toggle the default from 'charge on blindly with no entropy' to 'block indefinitely.' This default is safer, but may cause frustration. Embedded system designers using FreeBSD have several options. The most obvious is to plan to have a small writable NVRAM or NAND to persist entropy, like larger systems. Early entropy can be fed from any loader, or by writing directly to /dev/random during boot. Some embedded SoCs now provide a fast hardware entropy source; this would also work for quickly seeding Fortuna. A 3rd option would be creating an embedded-specific, more simplistic random module, like that designed by DJB in [1] (this design still requires a small rewritable media for forward secrecy). Finally, the least preferred option might be "nodevice random", although I plan to remove this in a subsequent revision. To help developers emulate the behavior of these embedded systems on ordinary workstations, the tunable kern.random.block_seeded_status was added. When set to 1, it blocks the random device. I attempted to document this change in random.4 and random.9 and ran into a bunch of out-of-date or irrelevant or inaccurate content and ended up rototilling those documents more than I intended to. Sorry. I think they're in a better state now. PR: 230875 Reviewed by: delphij, markm (earlier version) Approved by: secteam(delphij), devrandom(markm) Relnotes: yes Differential Revision: https://reviews.freebsd.org/D19744
2019-04-15 18:40:36 +00:00
To emulate embedded systems, developers may set the
.Va kern.random.block_seeded_status
tunable to 1 to verify boot does not require early availability of the
Add a section on different types of randomness, what the library functions we provide are good for and how /dev/random fits into this picture. Reviewed by: markm
2003-02-23 16:28:58 +00:00
.Nm
device.
Reference in New Issue Copy Permalink