bpf: poison dead stack slots

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As a sanity check poison stack slots that stack liveness determined
to be dead, so that any read from such slots will cause program rejection.
If stack liveness logic is incorrect the poison can cause
valid program to be rejected, but it also will prevent unsafe program
to be accepted.

Allow global subprogs "read" poisoned stack slots.
The static stack liveness determined that subprog doesn't read certain
stack slots, but sizeof(arg_type) based global subprog validation
isn't accurate enough to know which slots will actually be read by
the callee, so it needs to check full sizeof(arg_type) at the caller.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260410-patch-set-v4-14-5d4eecb343db@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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This commit is contained in:

Alexei Starovoitov 2026-04-10 13:56:05 -07:00

parent 27417e5eb9

commit 2cb27158ad

4 changed files with 70 additions and 27 deletions

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1

include/linux/bpf_verifier.h

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5

kernel/bpf/log.c

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89

kernel/bpf/verifier.c

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2

tools/testing/selftests/bpf/progs/verifier_spill_fill.c

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