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2660b9d477
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
39 lines
1011 B
C
39 lines
1011 B
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2025 Nandakumar Edamana */
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#include <linux/bpf.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include "bpf_misc.h"
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/* Intended to test the abstract multiplication technique(s) used by
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* the verifier. Using assembly to avoid compiler optimizations.
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*/
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SEC("fentry/bpf_fentry_test1")
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void BPF_PROG(mul_precise, int x)
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{
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/* First, force the verifier to be uncertain about the value:
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* unsigned int a = (bpf_get_prandom_u32() & 0x2) | 0x1;
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*
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* Assuming the verifier is using tnum, a must be tnum{.v=0x1, .m=0x2}.
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* Then a * 0x3 would be m0m1 (m for uncertain). Added imprecision
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* would cause the following to fail, because the required return value
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* is 0:
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* return (a * 0x3) & 0x4);
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*/
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asm volatile ("\
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call %[bpf_get_prandom_u32];\
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r0 &= 0x2;\
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r0 |= 0x1;\
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r0 *= 0x3;\
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r0 &= 0x4;\
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if r0 != 0 goto l0_%=;\
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r0 = 0;\
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goto l1_%=;\
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l0_%=:\
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r0 = 1;\
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l1_%=:\
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" :
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: __imm(bpf_get_prandom_u32)
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: __clobber_all);
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}
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