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| author | Jiayuan Chen <jiayuan.chen@linux.dev> | 2026-08-19 20:58:30 +0800 |
|---|---|---|
| committer | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2026-08-20 20:44:16 +0200 |
| commit | 7ee2f20bf20ed59fb269a260c4c4aff1e67f1b7c (patch) | |
| tree | 6b89842795519fce7698a35d8777bcfb98d7bf07 | |
| parent | 150aeba624e8b7cac51c39440d7e8e1fd11de9a0 (diff) | |
selftests/bpf: Add reg-invariants test for speculative pointer arithmetic
An unprivileged socket filter does variable pointer arithmetic on a
PTR_TO_MAP_VALUE whose offset collapses to a constant. The Spectre-v1
speculative path used to snapshot the pointer with a const offset and an
unbounded r32, which tripped reg_bounds_sanity_check() on the following
register move.
Mark the test __success_unpriv (the speculative path only runs
unprivileged) and flag it BPF_F_TEST_REG_INVARIANTS so the invariant
violation becomes a hard load failure. The unprivileged run fails without
the verifier fix and passes with it:
verifier_bounds/spec_ptr_alu_const_offset @unpriv:FAIL # without fix
verifier_bounds/spec_ptr_alu_const_offset @unpriv:OK # with fix
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260819125840.286434-2-jiayuan.chen@linux.dev
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
| -rw-r--r-- | tools/testing/selftests/bpf/progs/verifier_bounds.c | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds.c b/tools/testing/selftests/bpf/progs/verifier_bounds.c index 1a273e416fed..df8d5309657e 100644 --- a/tools/testing/selftests/bpf/progs/verifier_bounds.c +++ b/tools/testing/selftests/bpf/progs/verifier_bounds.c @@ -2267,6 +2267,47 @@ __naked void deduce64_from_32_wrapping_32bit(void) : __clobber_all); } +/* + * Unprivileged variable pointer arithmetic on a PTR_TO_MAP_VALUE whose + * offset collapses to a constant. The Spectre-v1 speculative path snapshots + * the pointer while its r32 has just been blanked but its offset not yet + * synced; the following register move used to trip reg_bounds_sanity_check() + * ("const subreg tnum out of sync with range bounds"). With + * BPF_F_TEST_REG_INVARIANTS that violation turns into a load failure, so the + * unprivileged program must still load. + */ +SEC("socket") +__success __success_unpriv +__flag(BPF_F_TEST_REG_INVARIANTS) +__naked void spec_ptr_alu_const_offset(void) +{ + asm volatile (" \ + call %[bpf_ktime_get_ns]; \ + *(u64*)(r10 - 16) = r0; \ + r1 = 0; \ + *(u64*)(r10 - 8) = r1; \ + r2 = r10; \ + r2 += -8; \ + r1 = %[map_hash_8b] ll; \ + call %[bpf_map_lookup_elem]; \ + if r0 == 0 goto l0_%=; \ + r1 = *(u64*)(r10 - 16); \ + r2 = 0x40000000; \ + if r1 > r2 goto l0_%=; \ + if r1 s> 1 goto l0_%=; /* r1 in [0, 1] */ \ + r0 += r1; /* ptr += bounded scalar */ \ + r9 = r0; /* used to trip the warning */ \ + *(u8*)(r0 + 0) = r1; \ +l0_%=: r0 = 0; \ + exit; \ + " + : + : __imm(bpf_ktime_get_ns), + __imm(bpf_map_lookup_elem), + __imm_addr(map_hash_8b) + : __clobber_all); +} + /* Check that range_within() compares cnum ranges, not min/max projections. */ SEC("socket") __failure __msg("div by zero") |