in the future in a backward compatible (API and ABI) way.
The cap_rights_t represents capability rights. We used to use one bit to
represent one right, but we are running out of spare bits. Currently the new
structure provides place for 114 rights (so 50 more than the previous
cap_rights_t), but it is possible to grow the structure to hold at least 285
rights, although we can make it even larger if 285 rights won't be enough.
The structure definition looks like this:
struct cap_rights {
uint64_t cr_rights[CAP_RIGHTS_VERSION + 2];
};
The initial CAP_RIGHTS_VERSION is 0.
The top two bits in the first element of the cr_rights[] array contain total
number of elements in the array - 2. This means if those two bits are equal to
0, we have 2 array elements.
The top two bits in all remaining array elements should be 0.
The next five bits in all array elements contain array index. Only one bit is
used and bit position in this five-bits range defines array index. This means
there can be at most five array elements in the future.
To define new right the CAPRIGHT() macro must be used. The macro takes two
arguments - an array index and a bit to set, eg.
#define CAP_PDKILL CAPRIGHT(1, 0x0000000000000800ULL)
We still support aliases that combine few rights, but the rights have to belong
to the same array element, eg:
#define CAP_LOOKUP CAPRIGHT(0, 0x0000000000000400ULL)
#define CAP_FCHMOD CAPRIGHT(0, 0x0000000000002000ULL)
#define CAP_FCHMODAT (CAP_FCHMOD | CAP_LOOKUP)
There is new API to manage the new cap_rights_t structure:
cap_rights_t *cap_rights_init(cap_rights_t *rights, ...);
void cap_rights_set(cap_rights_t *rights, ...);
void cap_rights_clear(cap_rights_t *rights, ...);
bool cap_rights_is_set(const cap_rights_t *rights, ...);
bool cap_rights_is_valid(const cap_rights_t *rights);
void cap_rights_merge(cap_rights_t *dst, const cap_rights_t *src);
void cap_rights_remove(cap_rights_t *dst, const cap_rights_t *src);
bool cap_rights_contains(const cap_rights_t *big, const cap_rights_t *little);
Capability rights to the cap_rights_init(), cap_rights_set(),
cap_rights_clear() and cap_rights_is_set() functions are provided by
separating them with commas, eg:
cap_rights_t rights;
cap_rights_init(&rights, CAP_READ, CAP_WRITE, CAP_FSTAT);
There is no need to terminate the list of rights, as those functions are
actually macros that take care of the termination, eg:
#define cap_rights_set(rights, ...) \
__cap_rights_set((rights), __VA_ARGS__, 0ULL)
void __cap_rights_set(cap_rights_t *rights, ...);
Thanks to using one bit as an array index we can assert in those functions that
there are no two rights belonging to different array elements provided
together. For example this is illegal and will be detected, because CAP_LOOKUP
belongs to element 0 and CAP_PDKILL to element 1:
cap_rights_init(&rights, CAP_LOOKUP | CAP_PDKILL);
Providing several rights that belongs to the same array's element this way is
correct, but is not advised. It should only be used for aliases definition.
This commit also breaks compatibility with some existing Capsicum system calls,
but I see no other way to do that. This should be fine as Capsicum is still
experimental and this change is not going to 9.x.
Sponsored by: The FreeBSD Foundation
performance... Use SSE2 instructions for calculating the XTS tweek
factor... Let the compiler do more work and handle register allocation
by using intrinsics, now only the key schedule is in assembly...
Replace .byte hard coded instructions w/ the proper instructions now
that both clang and gcc support them...
On my machine, pulling the code to userland I saw performance go from
~150MB/sec to 2GB/sec in XTS mode. GELI on GNOP saw a more modest
increase of about 3x due to other system overhead (geom and
opencrypto)...
These changes allow almost full disk io rate w/ geli...
Reviewed by: -current, -security
Thanks to: Mike Hamburg for the XTS tweek algorithm
Use this new driver for both PV and HVM instances.
This driver requires a Xen hypervisor that supports vector callbacks,
VCPUOP hypercalls, and reports that it has a "safe PV clock".
New timer driver:
Submitted by: will
Sponsored by: Spectra Logic Corporation
PV port to new driver, and bug fixes:
Submitted by: Roger Pau Monné
Sponsored by: Citrix Systems R&D
sys/dev/xen/timer/timer.c:
- Register a PV timer device driver which (currently)
implements device_{identify,probe,attach} and stubs
device_detach. The detach routine requires functionality
not provided by timecounters(4). The suspend and resume
routines need additional work (due to Xen requiring that
the hypercalls be executed on the target VCPU), and aren't
needed for our purposes.
- Make sure there can only be one device instance of this
driver, and that it only registers one eventtimers(4) and
one timecounters(4) device interface. Make both interfaces
use PCPU data as needed.
- Match, with a few style cleanups & API differences, the
Xen versions of the "fetch time" functions.
- Document the magic scale_delta() better for the i386 version.
- When registering the event timer, bind a separate event
channel for the timer VIRQ to the device's event timer
interrupt handler for each active VCPU. Describe each
interrupt as "xen_et:c%d", so they can be identified per
CPU in "vmstat -i" or "show intrcnt" in KDB.
- When scheduling a timer into the hypervisor, try up to
60 times if the hypervisor rejects the time as being in
the past. In the common case, this retry shouldn't happen,
and if it does, it should only happen once. This is
because the event timer advertises a minimum period of
100usec, which is only less than the usual hypercall round
trip time about 1 out of every 100 tries. (Unlike other
similar drivers, this one actually checks whether the
hypervisor accepted the singleshot timer set hypercall.)
- Implement a RTC PV clock based on the hypervisor wallclock.
sys/conf/files:
- Add dev/xen/timer/timer.c if the kernel configuration
includes either the XEN or XENHVM options.
sys/conf/files.i386:
sys/i386/include/xen/xen_clock_util.h:
sys/i386/xen/clock.c:
sys/i386/xen/xen_clock_util.c:
sys/i386/xen/mp_machdep.c:
sys/i386/xen/xen_rtc.c:
- Remove previous PV timer used in i386 XEN PV kernels, the
new timer introduced in this change is used instead (so
we share the same code between PVHVM and PV).
MFC after: 2 weeks
Re-structure Xen HVM support so that:
- Xen is detected and hypercalls can be performed very
early in system startup.
- Xen interrupt services are implemented using FreeBSD's native
interrupt delivery infrastructure.
- the Xen interrupt service implementation is shared between PV
and HVM guests.
- Xen interrupt handlers can optionally use a filter handler
in order to avoid the overhead of dispatch to an interrupt
thread.
- interrupt load can be distributed among all available CPUs.
- the overhead of accessing the emulated local and I/O apics
on HVM is removed for event channel port events.
- a similar optimization can eventually, and fairly easily,
be used to optimize MSI.
Early Xen detection, HVM refactoring, PVHVM interrupt infrastructure,
and misc Xen cleanups:
Sponsored by: Spectra Logic Corporation
Unification of PV & HVM interrupt infrastructure, bug fixes,
and misc Xen cleanups:
Submitted by: Roger Pau Monné
Sponsored by: Citrix Systems R&D
sys/x86/x86/local_apic.c:
sys/amd64/include/apicvar.h:
sys/i386/include/apicvar.h:
sys/amd64/amd64/apic_vector.S:
sys/i386/i386/apic_vector.s:
sys/amd64/amd64/machdep.c:
sys/i386/i386/machdep.c:
sys/i386/xen/exception.s:
sys/x86/include/segments.h:
Reserve IDT vector 0x93 for the Xen event channel upcall
interrupt handler. On Hypervisors that support the direct
vector callback feature, we can request that this vector be
called directly by an injected HVM interrupt event, instead
of a simulated PCI interrupt on the Xen platform PCI device.
This avoids all of the overhead of dealing with the emulated
I/O APIC and local APIC. It also means that the Hypervisor
can inject these events on any CPU, allowing upcalls for
different ports to be handled in parallel.
sys/amd64/amd64/mp_machdep.c:
sys/i386/i386/mp_machdep.c:
Map Xen per-vcpu area during AP startup.
sys/amd64/include/intr_machdep.h:
sys/i386/include/intr_machdep.h:
Increase the FreeBSD IRQ vector table to include space
for event channel interrupt sources.
sys/amd64/include/pcpu.h:
sys/i386/include/pcpu.h:
Remove Xen HVM per-cpu variable data. These fields are now
allocated via the dynamic per-cpu scheme. See xen_intr.c
for details.
sys/amd64/include/xen/hypercall.h:
sys/dev/xen/blkback/blkback.c:
sys/i386/include/xen/xenvar.h:
sys/i386/xen/clock.c:
sys/i386/xen/xen_machdep.c:
sys/xen/gnttab.c:
Prefer FreeBSD primatives to Linux ones in Xen support code.
sys/amd64/include/xen/xen-os.h:
sys/i386/include/xen/xen-os.h:
sys/xen/xen-os.h:
sys/dev/xen/balloon/balloon.c:
sys/dev/xen/blkback/blkback.c:
sys/dev/xen/blkfront/blkfront.c:
sys/dev/xen/console/xencons_ring.c:
sys/dev/xen/control/control.c:
sys/dev/xen/netback/netback.c:
sys/dev/xen/netfront/netfront.c:
sys/dev/xen/xenpci/xenpci.c:
sys/i386/i386/machdep.c:
sys/i386/include/pmap.h:
sys/i386/include/xen/xenfunc.h:
sys/i386/isa/npx.c:
sys/i386/xen/clock.c:
sys/i386/xen/mp_machdep.c:
sys/i386/xen/mptable.c:
sys/i386/xen/xen_clock_util.c:
sys/i386/xen/xen_machdep.c:
sys/i386/xen/xen_rtc.c:
sys/xen/evtchn/evtchn_dev.c:
sys/xen/features.c:
sys/xen/gnttab.c:
sys/xen/gnttab.h:
sys/xen/hvm.h:
sys/xen/xenbus/xenbus.c:
sys/xen/xenbus/xenbus_if.m:
sys/xen/xenbus/xenbusb_front.c:
sys/xen/xenbus/xenbusvar.h:
sys/xen/xenstore/xenstore.c:
sys/xen/xenstore/xenstore_dev.c:
sys/xen/xenstore/xenstorevar.h:
Pull common Xen OS support functions/settings into xen/xen-os.h.
sys/amd64/include/xen/xen-os.h:
sys/i386/include/xen/xen-os.h:
sys/xen/xen-os.h:
Remove constants, macros, and functions unused in FreeBSD's Xen
support.
sys/xen/xen-os.h:
sys/i386/xen/xen_machdep.c:
sys/x86/xen/hvm.c:
Introduce new functions xen_domain(), xen_pv_domain(), and
xen_hvm_domain(). These are used in favor of #ifdefs so that
FreeBSD can dynamically detect and adapt to the presence of
a hypervisor. The goal is to have an HVM optimized GENERIC,
but more is necessary before this is possible.
sys/amd64/amd64/machdep.c:
sys/dev/xen/xenpci/xenpcivar.h:
sys/dev/xen/xenpci/xenpci.c:
sys/x86/xen/hvm.c:
sys/sys/kernel.h:
Refactor magic ioport, Hypercall table and Hypervisor shared
information page setup, and move it to a dedicated HVM support
module.
HVM mode initialization is now triggered during the
SI_SUB_HYPERVISOR phase of system startup. This currently
occurs just after the kernel VM is fully setup which is
just enough infrastructure to allow the hypercall table
and shared info page to be properly mapped.
sys/xen/hvm.h:
sys/x86/xen/hvm.c:
Add definitions and a method for configuring Hypervisor event
delievery via a direct vector callback.
sys/amd64/include/xen/xen-os.h:
sys/x86/xen/hvm.c:
sys/conf/files:
sys/conf/files.amd64:
sys/conf/files.i386:
Adjust kernel build to reflect the refactoring of early
Xen startup code and Xen interrupt services.
sys/dev/xen/blkback/blkback.c:
sys/dev/xen/blkfront/blkfront.c:
sys/dev/xen/blkfront/block.h:
sys/dev/xen/control/control.c:
sys/dev/xen/evtchn/evtchn_dev.c:
sys/dev/xen/netback/netback.c:
sys/dev/xen/netfront/netfront.c:
sys/xen/xenstore/xenstore.c:
sys/xen/evtchn/evtchn_dev.c:
sys/dev/xen/console/console.c:
sys/dev/xen/console/xencons_ring.c
Adjust drivers to use new xen_intr_*() API.
sys/dev/xen/blkback/blkback.c:
Since blkback defers all event handling to a taskqueue,
convert this task queue to a "fast" taskqueue, and schedule
it via an interrupt filter. This avoids an unnecessary
ithread context switch.
sys/xen/xenstore/xenstore.c:
The xenstore driver is MPSAFE. Indicate as much when
registering its interrupt handler.
sys/xen/xenbus/xenbus.c:
sys/xen/xenbus/xenbusvar.h:
Remove unused event channel APIs.
sys/xen/evtchn.h:
Remove all kernel Xen interrupt service API definitions
from this file. It is now only used for structure and
ioctl definitions related to the event channel userland
device driver.
Update the definitions in this file to match those from
NetBSD. Implementing this interface will be necessary for
Dom0 support.
sys/xen/evtchn/evtchnvar.h:
Add a header file for implemenation internal APIs related
to managing event channels event delivery. This is used
to allow, for example, the event channel userland device
driver to access low-level routines that typical kernel
consumers of event channel services should never access.
sys/xen/interface/event_channel.h:
sys/xen/xen_intr.h:
Standardize on the evtchn_port_t type for referring to
an event channel port id. In order to prevent low-level
event channel APIs from leaking to kernel consumers who
should not have access to this data, the type is defined
twice: Once in the Xen provided event_channel.h, and again
in xen/xen_intr.h. The double declaration is protected by
__XEN_EVTCHN_PORT_DEFINED__ to ensure it is never declared
twice within a given compilation unit.
sys/xen/xen_intr.h:
sys/xen/evtchn/evtchn.c:
sys/x86/xen/xen_intr.c:
sys/dev/xen/xenpci/evtchn.c:
sys/dev/xen/xenpci/xenpcivar.h:
New implementation of Xen interrupt services. This is
similar in many respects to the i386 PV implementation with
the exception that events for bound to event channel ports
(i.e. not IPI, virtual IRQ, or physical IRQ) are further
optimized to avoid mask/unmask operations that aren't
necessary for these edge triggered events.
Stubs exist for supporting physical IRQ binding, but will
need additional work before this implementation can be
fully shared between PV and HVM.
sys/amd64/amd64/mp_machdep.c:
sys/i386/i386/mp_machdep.c:
sys/i386/xen/mp_machdep.c
sys/x86/xen/hvm.c:
Add support for placing vcpu_info into an arbritary memory
page instead of using HYPERVISOR_shared_info->vcpu_info.
This allows the creation of domains with more than 32 vcpus.
sys/i386/i386/machdep.c:
sys/i386/xen/clock.c:
sys/i386/xen/xen_machdep.c:
sys/i386/xen/exception.s:
Add support for new event channle implementation.
dynamic translation so that their arguments match the definitions for
these providers in Solaris and illumos. Thus, existing scripts for these
providers should work unmodified on FreeBSD.
Tested by: gnn, hiren
MFC after: 1 month
* It's not meant to be used in a real system, it's there to show how
the basics of how to create interfaces for random_adaptors. Perhaps
it should belong in a manual page
2) Move probe.c's functionality in to random_adaptors.c
* rename random_ident_hardware() to random_adaptor_choose()
3) Introduce a new way to choose (or select) random_adaptors via tunable
"rngs_want" It's a list of comma separated names of adaptors, ordered
by preferences. I.e.:
rngs_want="yarrow,rdrand"
Such setting would cause yarrow to be preferred to rdrand. If neither of
them are available (or registered), then system will default to
something reasonable (currently yarrow). If yarrow is not present, then
we fall back to the adaptor that's first on the list of registered
adaptors.
4) Introduce a way where RNGs can play a role of entropy source. This is
mostly useful for HW rngs.
The way I envision this is that every HW RNG will use this
functionality by default. Functionality to disable this is also present.
I have an example of how to use this in random_adaptor_example.c (see
modload event, and init function)
5) fix kern.random.adaptors from
kern.random.adaptors: yarrowpanicblock
to
kern.random.adaptors: yarrow,panic,block
6) add kern.random.active_adaptor to indicate currently selected
adaptor:
root@freebsd04:~ # sysctl kern.random.active_adaptor
kern.random.active_adaptor: yarrow
Submitted by: Arthur Mesh <arthurmesh@gmail.com>
(sys/dev/iscsi_initiator/ instead of sys/dev/iscsi/initiator/), to make
room for the new one. This is also more logical location (kernel module
being named iscsi_initiator.ko, for example). There is no ongoing work
on this I know of, so it shouldn't make life harder for anyone.
There are no functional changes, apart from "svn mv" and adjusting paths.
Basic support for extents was implemented by Zheng Liu as part
of his Google Summer of Code in 2010. This support is read-only
at this time.
In addition to extents we also support the huge_file extension
for read-only purposes. This works nicely with the additional
support for birthtime/nanosec timestamps and dir_index that
have been added lately.
The implementation may not work for all ext4 filesystems as
it doesn't support some features that are being enabled by
default on recent linux like flex_bg. Nevertheless, the feature
should be very useful for migration or simple access in
filesystems that have been converted from ext2/3 or don't use
incompatible features.
Special thanks to Zheng Liu for his dedication and continued
work to support ext2 in FreeBSD.
Submitted by: Zheng Liu (lz@)
Reviewed by: Mike Ma, Christoph Mallon (previous version)
Sponsored by: Google Inc.
MFC after: 3 weeks
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)
(or svnliteversion) in the current lookup path is not what
was used to check out the tree. If an incompatible version
is used, the svn revision number is not reported in uname(1).
Run ${svnversion} on newvers.sh itself when evaluating if the
svn(1) in use is compatible with the tree. Fallback to an
empty ${svnversion} if necessary.
With this change, svnliteversion from base is only used
if no compatible svnversion is found, so with this change,
the version of svn(1) from the ports tree is evaluated first.
Requested by: many
MFC after: 3 days
X-MFC-To: stable/9, releng/9.2 only
Do this by forcing inclusion of
sys/cddl/compat/opensolaris/sys/debug_compat.h
via -include option into all source files from OpenSolaris.
Note that this -include option must always be after -include opt_global.h.
Additionally, remove forced definition of DEBUG for some modules and fix
their build without DEBUG.
Also, meaning of DEBUG was overloaded to enable WITNESS support for some
OpenSolaris (primarily ZFS) locks. Now this overloading is removed and
that use of DEBUG is replaced with a new option OPENSOLARIS_WITNESS.
MFC after: 17 days
the tree version, for example if the tree is checked out with an
outdated svn from ports, but the base system svnlite is built.
Approved by: kib (mentor)
Support chipsets are the Realtek RTL8188SU, RTL8191SU, and RTL8192SU.
Many thanks to Idwer Vollering for porting/writing the man page and for
testing.
Reviewed by: adrian, hselasky
Obtained from: OpenBSD
Tested by: kevlo, Idwer Vollering <vidwer at gmail.com>
* Make Yarrow an optional kernel component -- enabled by "YARROW_RNG" option.
The files sha2.c, hash.c, randomdev_soft.c and yarrow.c comprise yarrow.
* random(4) device doesn't really depend on rijndael-*. Yarrow, however, does.
* 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: obrien
The original API calls for pow2ns, however the new APIs from
Linux call for seconds.
We need to be able to convert to/from 2^Nns to seconds in both
userland and kernel to fix this and properly compare units.
all T4 and T5 based cards and is useful for analyzing TSO, LRO, TOE, and
for general purpose monitoring without tapping any cxgbe or cxl ifnet
directly.
Tracers on the T4/T5 chips provide access to Ethernet frames exactly as
they were received from or transmitted on the wire. On transmit, a
tracer will capture a frame after TSO segmentation, hw VLAN tag
insertion, hw L3 & L4 checksum insertion, etc. It will also capture
frames generated by the TCP offload engine (TOE traffic is normally
invisible to the kernel). On receive, a tracer will capture a frame
before hw VLAN extraction, runt filtering, other badness filtering,
before the steering/drop/L2-rewrite filters or the TOE have had a go at
it, and of course before sw LRO in the driver.
There are 4 tracers on a chip. A tracer can trace only in one direction
(tx or rx). For now cxgbetool will set up tracers to capture the first
128B of every transmitted or received frame on a given port. This is a
small subset of what the hardware can do. A pseudo ifnet with the same
name as the nexus driver (t4nex0 or t5nex0) will be created for tracing.
The data delivered to this ifnet is an additional copy made inside the
chip. Normal delivery to cxgbe<n> or cxl<n> will be made as usual.
/* watch cxl0, which is the first port hanging off t5nex0. */
# cxgbetool t5nex0 tracer 0 tx0 (watch what cxl0 is transmitting)
# cxgbetool t5nex0 tracer 1 rx0 (watch what cxl0 is receiving)
# cxgbetool t5nex0 tracer list
# tcpdump -i t5nex0 <== all that cxl0 sees and puts on the wire
If you were doing TSO, a tcpdump on cxl0 may have shown you ~64K
"frames" with no L3/L4 checksum but this will show you the frames that
were actually transmitted.
/* all done */
# cxgbetool t5nex0 tracer 0 disable
# cxgbetool t5nex0 tracer 1 disable
# cxgbetool t5nex0 tracer list
# ifconfig t5nex0 destroy
This time it is for a git mirror that stores svn revisions as
git notes, e.g. https://github.com/freebsd/freebsd
MFC after: 10 days
Sponsored by: HybridCluster
As part of this commit, add an nvme_strvis() function which borrows
heavily from cam_strvis(). This will allow stripping of
leading/trailing whitespace and also handle unprintable characters
in model/serial numbers. This function goes into a new nvme_util.c
file which is used by both the driver and nvmecontrol.
Sponsored by: Intel
Reviewed by: carl
MFC after: 3 days
make the ARM EABI the default ABI on arm, armeb, armv6 and armv6eb.
This is intended to be the default ABI from now on with the old ABI to be
retired. Because of this all users are strongly suggested to upgrade to the
ARM EABI.
As the two ABIs are incompatible it is unlikely upgrading in place will
work. Users should perform a full backup and either use an external machine
to upgrade, or install to an alternative location on their media. They
should also reinstall all ports or packages when these are available.
The only known issues are:
- pkg incorrectly detects the ABI. This is fixed upstream, and will a
patch will be made to the port.
- GDB can have issues with executables built with clang.
__FreeBSD_version has been bumped.
information into the ISN (initial sequence number) without the additional
use of timestamp bits and switching to the very fast and cryptographically
strong SipHash-2-4 MAC hash algorithm to protect the SYN cookie against
forgeries.
The purpose of SYN cookies is to encode all necessary session state in
the 32 bits of our initial sequence number to avoid storing any information
locally in memory. This is especially important when under heavy spoofed
SYN attacks where we would either run out of memory or the syncache would
fill with bogus connection attempts swamping out legitimate connections.
The original SYN cookies method only stored an indexed MSS values in the
cookie. This isn't sufficient anymore and breaks down in the presence of
WSCALE information which is only exchanged during SYN and SYN-ACK. If we
can't keep track of it then we may severely underestimate the available
send or receive window. This is compounded with large windows whose size
information on the TCP segment header is even lower numerically. A number
of years back SYN cookies were extended to store the additional state in
the TCP timestamp fields, if available on a connection. While timestamps
are common among the BSD, Linux and other *nix systems Windows never enabled
them by default and thus are not present for the vast majority of clients
seen on the Internet.
The common parameters used on TCP sessions have changed quite a bit since
SYN cookies very invented some 17 years ago. Today we have a lot more
bandwidth available making the use window scaling almost mandatory. Also
SACK has become standard making recovering from packet loss much more
efficient.
This change moves all necessary information into the ISS removing the need
for timestamps. Both the MSS (16 bits) and send WSCALE (4 bits) are stored
in 3 bit indexed form together with a single bit for SACK. While this is
significantly less than the original range, it is sufficient to encode all
common values with minimal rounding.
The MSS depends on the MTU of the path and with the dominance of ethernet
the main value seen is around 1460 bytes. Encapsulations for DSL lines
and some other overheads reduce it by a few more bytes for many connections
seen. Rounding down to the next lower value in some cases isn't a problem
as we send only slightly more packets for the same amount of data.
The send WSCALE index is bit more tricky as rounding down under-estimates
the available send space available towards the remote host, however a small
number values dominate and are carefully selected again.
The receive WSCALE isn't encoded at all but recalculated based on the local
receive socket buffer size when a valid SYN cookie returns. A listen socket
buffer size is unlikely to change while active.
The index values for MSS and WSCALE are selected for minimal rounding errors
based on large traffic surveys. These values have to be periodically
validated against newer traffic surveys adjusting the arrays tcp_sc_msstab[]
and tcp_sc_wstab[] if necessary.
In addition the hash MAC to protect the SYN cookies is changed from MD5
to SipHash-2-4, a much faster and cryptographically secure algorithm.
Reviewed by: dwmalone
Tested by: Fabian Keil <fk@fabiankeil.de>
