Merge branch 'New BPF helpers to accelerate synproxy'

Maxim Mikityanskiy says:

====================

The first patch of this series is a documentation fix.

The second patch allows BPF helpers to accept memory regions of fixed
size without doing runtime size checks.

The two next patches add new functionality that allows XDP to
accelerate iptables synproxy.

v1 of this series [1] used to include a patch that exposed conntrack
lookup to BPF using stable helpers. It was superseded by series [2] by
Kumar Kartikeya Dwivedi, which implements this functionality using
unstable helpers.

The third patch adds new helpers to issue and check SYN cookies without
binding to a socket, which is useful in the synproxy scenario.

The fourth patch adds a selftest, which includes an XDP program and a
userspace control application. The XDP program uses socketless SYN
cookie helpers and queries conntrack status instead of socket status.
The userspace control application allows to tune parameters of the XDP
program. This program also serves as a minimal example of usage of the
new functionality.

The last two patches expose the new helpers to TC BPF and extend the
selftest.

The draft of the new functionality was presented on Netdev 0x15 [3].

v2 changes:

Split into two series, submitted bugfixes to bpf, dropped the conntrack
patches, implemented the timestamp cookie in BPF using bpf_loop, dropped
the timestamp cookie patch.

v3 changes:

Moved some patches from bpf to bpf-next, dropped the patch that changed
error codes, split the new helpers into IPv4/IPv6, added verifier
functionality to accept memory regions of fixed size.

v4 changes:

Converted the selftest to the test_progs runner. Replaced some
deprecated functions in xdp_synproxy userspace helper.

v5 changes:

Fixed a bug in the selftest. Added questionable functionality to support
new helpers in TC BPF, added selftests for it.

v6 changes:

Wrap the new helpers themselves into #ifdef CONFIG_SYN_COOKIES, replaced
fclose with pclose and fixed the MSS for IPv6 in the selftest.

v7 changes:

Fixed the off-by-one error in indices, changed the section name to
"xdp", added missing kernel config options to vmtest in CI.

v8 changes:

Properly rebased, dropped the first patch (the same change was applied
by someone else), updated the cover letter.

v9 changes:

Fixed selftests for no_alu32.

v10 changes:

Selftests for s390x were blacklisted due to lack of support of kfunc,
rebased the series, split selftests to separate commits, created
ARG_PTR_TO_FIXED_SIZE_MEM and packed arg_size, addressed the rest of
comments.

[1]: https://lore.kernel.org/bpf/20211020095815.GJ28644@breakpoint.cc/t/
[2]: https://lore.kernel.org/bpf/20220114163953.1455836-1-memxor@gmail.com/
[3]: https://netdevconf.info/0x15/session.html?Accelerating-synproxy-with-XDP
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>