diff options
| author | Nandakumar Edamana <nandakumar@nandakumar.co.in> | 2025-08-26 09:15:24 +0530 |
|---|---|---|
| committer | Andrii Nakryiko <andrii@kernel.org> | 2025-08-27 15:00:31 -0700 |
| commit | 2660b9d477501c3dbb09705640b70d0a80072f0c (patch) | |
| tree | ea09ad0d76a3193e9add86a6841039005dbb041c /tools/testing/selftests/bpf/progs/verifier_mul.c | |
| parent | 1df7dad4d5c49335b72e26d833def960b2de76e3 (diff) | |
bpf: Add selftest to check the verifier's abstract multiplication
Add new selftest to test the abstract multiplication technique(s) used
by the verifier, following the recent improvement in tnum
multiplication (tnum_mul). One of the newly added programs,
verifier_mul/mul_precise, results in a false positive with the old
tnum_mul, while the program passes with the latest one.
Signed-off-by: Nandakumar Edamana <nandakumar@nandakumar.co.in>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Harishankar Vishwanathan <harishankar.vishwanathan@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20250826034524.2159515-2-nandakumar@nandakumar.co.in
Diffstat (limited to 'tools/testing/selftests/bpf/progs/verifier_mul.c')
| -rw-r--r-- | tools/testing/selftests/bpf/progs/verifier_mul.c | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/verifier_mul.c b/tools/testing/selftests/bpf/progs/verifier_mul.c new file mode 100644 index 000000000000..7145fe3351d5 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/verifier_mul.c @@ -0,0 +1,38 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2025 Nandakumar Edamana */ +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> +#include "bpf_misc.h" + +/* Intended to test the abstract multiplication technique(s) used by + * the verifier. Using assembly to avoid compiler optimizations. + */ +SEC("fentry/bpf_fentry_test1") +void BPF_PROG(mul_precise, int x) +{ + /* First, force the verifier to be uncertain about the value: + * unsigned int a = (bpf_get_prandom_u32() & 0x2) | 0x1; + * + * Assuming the verifier is using tnum, a must be tnum{.v=0x1, .m=0x2}. + * Then a * 0x3 would be m0m1 (m for uncertain). Added imprecision + * would cause the following to fail, because the required return value + * is 0: + * return (a * 0x3) & 0x4); + */ + asm volatile ("\ + call %[bpf_get_prandom_u32];\ + r0 &= 0x2;\ + r0 |= 0x1;\ + r0 *= 0x3;\ + r0 &= 0x4;\ + if r0 != 0 goto l0_%=;\ + r0 = 0;\ + goto l1_%=;\ +l0_%=:\ + r0 = 1;\ +l1_%=:\ +" : + : __imm(bpf_get_prandom_u32) + : __clobber_all); +} |