b546b57526
This commit updates tcp_custom_syncookie.c:tcp_parse_option() to use
explicit packet offset (ctx->off) for packet access instead of ever
moving pointer (ctx->ptr), this reduces verification complexity:
- the tcp_parse_option() is passed as a callback to bpf_loop();
- suppose a checkpoint is created each time at function entry;
- the ctx->ptr is tracked by verifier as PTR_TO_PACKET;
- the ctx->ptr is incremented in tcp_parse_option(),
thus umax_value field tracked for it is incremented as well;
- on each next iteration of tcp_parse_option()
checkpoint from a previous iteration can't be reused
for state pruning, because PTR_TO_PACKET registers are
considered equivalent only if old->umax_value >= cur->umax_value;
- on the other hand, the ctx->off is a SCALAR,
subject to widen_imprecise_scalars();
- it's exact bounds are eventually forgotten and it is tracked as
unknown scalar at entry to tcp_parse_option();
- hence checkpoints created at the start of the function eventually
converge.
The change is similar to one applied in [0] to xdp_synproxy_kern.c.
Comparing before and after with veristat yields following results:
File Insns (A) Insns (B) Insns (DIFF)
------------------------------- --------- --------- -----------------
test_tcp_custom_syncookie.bpf.o 466657 12423 -454234 (-97.34%)
[0] commit 977bc146d4eb ("selftests/bpf: track tcp payload offset as scalar in xdp_synproxy")
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240222150300.14909-2-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.