MFC r317208:

Syncoockies can be used in combination with the syncache. If the cache
overflows, syncookies are used.
This patch restricts the usage of syncookies in this case: accept
syncookies only if there was an overflow of the syncache recently.
This mitigates a problem reported in PR217637, where is syncookie was
accepted without any recent drops.
Thanks to glebius@ for suggesting an improvement.

PR: 217637
Reviewed by: gnn, glebius
Differential Revision: https://reviews.freebsd.org/D10272

MFC r292706:

Implementation of server-side TCP Fast Open (TFO) [RFC7413].

TFO is disabled by default in the kernel build. See the top comment
in sys/netinet/tcp_fastopen.c for implementation particulars.

Differential Revision: https://reviews.freebsd.org/D4350
Sponsored by: Verisign, Inc.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Introduce spares in the TCP syncache and timewait structures
so that fixed TCP_SIGNATURE handling can later be merged.

This is derived from follow-up work to SVN r183001 posted to
net@ on Sep 13 2008.

Approved by: re (gjb)

Unbreak VIMAGE by correctly naming the vnet pointer in struct tcp_syncache.

Reported by: trociny, rodrigc

Improve SYN cookies by encoding the MSS, WSCALE (window scaling) and SACK
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>

Change the syncache count reporting the current number of entries
from an unprotected u_int that reports garbage on SMP to a function
based sysctl obtaining the current value from UMA.

Also read back the actual cache_limit after page size rounding by UMA.

PR: kern/165879
MFC after: 2 weeks

- Updated TOE support in the kernel.

- Stateful TCP offload drivers for Terminator 3 and 4 (T3 and T4) ASICs.
These are available as t3_tom and t4_tom modules that augment cxgb(4)
and cxgbe(4) respectively. The cxgb/cxgbe drivers continue to work as
usual with or without these extra features.

- iWARP driver for Terminator 3 ASIC (kernel verbs). T4 iWARP in the
works and will follow soon.

Build-tested with make universe.

30s overview
============
What interfaces support TCP offload? Look for TOE4 and/or TOE6 in the
capabilities of an interface:
# ifconfig -m | grep TOE

Enable/disable TCP offload on an interface (just like any other ifnet
capability):
# ifconfig cxgbe0 toe
# ifconfig cxgbe0 -toe

Which connections are offloaded? Look for toe4 and/or toe6 in the
output of netstat and sockstat:
# netstat -np tcp | grep toe
# sockstat -46c | grep toe

Reviewed by: bz, gnn
Sponsored by: Chelsio communications.
MFC after: ~3 months (after 9.1, and after ensuring MFC is feasible)

Add spares to the network stack for FreeBSD-9:
- TCP keep* timers
- TCP UTO (adjust from what was there already)
- netmap
- route caching
- user cookie (temporary to allow for the real fix)

Slightly re-shuffle struct ifnet moving fields out of the middle
of spares and to better align.

Discussed with: rwatson (slightly earlier version)

Trim extra spaces before tabs.

Replace struct tcpopt with a proxy toeopt struct in the TOE driver interface to
the TCP syncache. This returns struct tcpopt to being private within the TCP
implementation, thus allowing it to be modified without ABI concerns.

The patch breaks the ABI. Bump __FreeBSD_version to 800103 accordingly. The cxgb
driver is the only TOE consumer affected by this change, and needs to be
recompiled along with the kernel.

Suggested by: rwatson
Reviewed by: rwatson, kmacy
Approved by: re (kensmith), kensmith (mentor temporarily unavailable)

Introduce an infrastructure for dismantling vnet instances.

Vnet modules and protocol domains may now register destructor
functions to clean up and release per-module state. The destructor
mechanisms can be triggered by invoking "vimage -d", or a future
equivalent command which will be provided via the new jail framework.

While this patch introduces numerous placeholder destructor functions,
many of those are currently incomplete, thus leaking memory or (even
worse) failing to stop all running timers. Many of such issues are
already known and will be incrementaly fixed over the next weeks in
smaller incremental commits.

Apart from introducing new fields in structs ifnet, domain, protosw
and vnet_net, which requires the kernel and modules to be rebuilt, this
change should have no impact on nooptions VIMAGE builds, since vnet
destructors can only be called in VIMAGE kernels. Moreover,
destructor functions should be in general compiled in only in
options VIMAGE builds, except for kernel modules which can be safely
kldunloaded at run time.

Bump __FreeBSD_version to 800097.
Reviewed by: bz, julian
Approved by: rwatson, kib (re), julian (mentor)

Unifdef MAC label pointer in syncache entries -- in general, ifdef'd
structure contents are a bad idea in the kernel for binary
compatibility reasons, and this is a single pointer that is now included
in compiles by default anyway due to options MAC being in GENERIC.

Permit buiding kernels with options VIMAGE, restricted to only a single
active network stack instance. Turning on options VIMAGE at compile
time yields the following changes relative to default kernel build:

1) V_ accessor macros for virtualized variables resolve to structure
fields via base pointers, instead of being resolved as fields in global
structs or plain global variables. As an example, V_ifnet becomes:

options VIMAGE: ((struct vnet_net *) vnet_net)->_ifnet
default build: vnet_net_0._ifnet
options VIMAGE_GLOBALS: ifnet

2) INIT_VNET_* macros will declare and set up base pointers to be used
by V_ accessor macros, instead of resolving to whitespace:

INIT_VNET_NET(ifp->if_vnet); becomes

struct vnet_net *vnet_net = (ifp->if_vnet)->mod_data[VNET_MOD_NET];

3) Memory for vnet modules registered via vnet_mod_register() is now
allocated at run time in sys/kern/kern_vimage.c, instead of per vnet
module structs being declared as globals. If required, vnet modules
can now request the framework to provide them with allocated bzeroed
memory by filling in the vmi_size field in their vmi_modinfo structures.

4) structs socket, ifnet, inpcbinfo, tcpcb and syncache_head are
extended to hold a pointer to the parent vnet. options VIMAGE builds
will fill in those fields as required.

5) curvnet is introduced as a new global variable in options VIMAGE
builds, always pointing to the default and only struct vnet.

6) struct sysctl_oid has been extended with additional two fields to
store major and minor virtualization module identifiers, oid_v_subs and
oid_v_mod. SYSCTL_V_* family of macros will fill in those fields
accordingly, and store the offset in the appropriate vnet container
struct in oid_arg1.
In sysctl handlers dealing with virtualized sysctls, the
SYSCTL_RESOLVE_V_ARG1() macro will compute the address of the target
variable and make it available in arg1 variable for further processing.

Unused fields in structs vnet_inet, vnet_inet6 and vnet_ipfw have
been deleted.

Reviewed by: bz, rwatson
Approved by: julian (mentor)

Move syncache flag definitions below data structure, compress some vertical
whitespace.

MFC after: pretty soon

Move some struct defs around. This is a prep step for Vimage.A
No real effect of this at this time.

add interface for external consumers to syncache_expand - rename syncache_add in a manner consistent with other bits intended for offload

Add interface for tcp offload to syncache:
- make neccessary changes to release offload resources when a syncache
entry is removed before connection establishment
- disable checks for offloaded connection where insufficient information
is available

Reviewed by: silby

Export the contents of the syncache to netstat.

Approved by: re (kensmith)
MFC after: 2 weeks