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selftests/bpf: add edge case backtracking logic test

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Add a dedicated selftests to try to set up conditions to have a state
with same first and last instruction index, but it actually is a loop
3->4->1->2->3. This confuses mark_chain_precision() if verifier doesn't
take into account jump history.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231110002638.4168352-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2023-11-09 16:26:38 -08:00 committed by Alexei Starovoitov
parent 4bb7ea946a
commit 62ccdb11d3
1 changed files with 40 additions and 0 deletions
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40
tools/testing/selftests/bpf/progs/verifier_precision.c
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@ -91,3 +91,43 @@ __naked int bpf_end_bswap(void)
}
#endif /* v4 instruction */
SEC("?raw_tp")
__success __log_level(2)
/*
* Without the bug fix there will be no history between "last_idx 3 first_idx 3"
* and "parent state regs=" lines. "R0_w=6" parts are here to help anchor
* expected log messages to the one specific mark_chain_precision operation.
*
* This is quite fragile: if verifier checkpointing heuristic changes, this
* might need adjusting.
*/
__msg("2: (07) r0 += 1 ; R0_w=6")
__msg("3: (35) if r0 >= 0xa goto pc+1")
__msg("mark_precise: frame0: last_idx 3 first_idx 3 subseq_idx -1")
__msg("mark_precise: frame0: regs=r0 stack= before 2: (07) r0 += 1")
__msg("mark_precise: frame0: regs=r0 stack= before 1: (07) r0 += 1")
__msg("mark_precise: frame0: regs=r0 stack= before 4: (05) goto pc-4")
__msg("mark_precise: frame0: regs=r0 stack= before 3: (35) if r0 >= 0xa goto pc+1")
__msg("mark_precise: frame0: parent state regs= stack=: R0_rw=P4")
__msg("3: R0_w=6")
__naked int state_loop_first_last_equal(void)
{
asm volatile (
"r0 = 0;"
"l0_%=:"
"r0 += 1;"
"r0 += 1;"
/* every few iterations we'll have a checkpoint here with
* first_idx == last_idx, potentially confusing precision
* backtracking logic
*/
"if r0 >= 10 goto l1_%=;" /* checkpoint + mark_precise */
"goto l0_%=;"
"l1_%=:"
"exit;"
::: __clobber_common
);
}
char _license[] SEC("license") = "GPL";