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random.4: Include description of knobs added in r346358

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Reported by:	ngie
Sponsored by:	Dell EMC Isilon
This commit is contained in:
Conrad Meyer 2019-04-19 17:15:58 +00:00
parent 2946a9415c
commit 55084da106
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=346399
1 changed files with 54 additions and 1 deletions
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55
share/man/man4/random.4
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@ -23,7 +23,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd April 15, 2019
.Dd April 19, 2019
.Dt RANDOM 4
.Os
.Sh NAME
@ -85,6 +85,10 @@ kern.random.harvest.mask_bin: 00000010000000111011111
kern.random.harvest.mask: 66015
kern.random.use_chacha20_cipher: 0
kern.random.random_sources: 'Intel Secure Key RNG'
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
.Ed
.Pp
Other than
@ -133,6 +137,55 @@ for more on the harvesting of entropy.
.It Pa /dev/random
.It Pa /dev/urandom
.El
.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
.Sh SEE ALSO
.Xr getrandom 2 ,
.Xr arc4random 3 ,