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| author | Yonghong Song <yonghong.song@linux.dev> | 2025-09-19 21:58:05 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2025-09-20 15:49:35 -0700 |
| commit | 5a427fddec5e76360725a0f03df3a2a003efbe2e (patch) | |
| tree | b63f75a662f9ad08559bcf6d2518c19c4214bcfd | |
| parent | 5612ea8b554375d45c14cbb0f8ea93ec5d172891 (diff) | |
selftests/bpf: Fix selftest verifier_arena_large failure
With latest llvm22, I got the following verification failure:
...
; int big_alloc2(void *ctx) @ verifier_arena_large.c:207
0: (b4) w6 = 1 ; R6_w=1
...
; if (err) @ verifier_arena_large.c:233
53: (56) if w6 != 0x0 goto pc+62 ; R6=0
54: (b7) r7 = -4 ; R7_w=-4
55: (18) r8 = 0x7f4000000000 ; R8_w=scalar()
57: (bf) r9 = addr_space_cast(r8, 0, 1) ; R8_w=scalar() R9_w=arena
58: (b4) w6 = 5 ; R6_w=5
; pg = page[i]; @ verifier_arena_large.c:238
59: (bf) r1 = r7 ; R1_w=-4 R7_w=-4
60: (07) r1 += 4 ; R1_w=0
61: (79) r2 = *(u64 *)(r9 +0) ; R2_w=scalar() R9_w=arena
; if (*pg != i) @ verifier_arena_large.c:239
62: (bf) r3 = addr_space_cast(r2, 0, 1) ; R2_w=scalar() R3_w=arena
63: (71) r3 = *(u8 *)(r3 +0) ; R3_w=scalar(smin=smin32=0,smax=umax=smax32=umax32=255,var_off=(0x0; 0xff))
64: (5d) if r1 != r3 goto pc+51 ; R1_w=0 R3_w=0
; bpf_arena_free_pages(&arena, (void __arena *)pg, 2); @ verifier_arena_large.c:241
65: (18) r1 = 0xff11000114548000 ; R1_w=map_ptr(map=arena,ks=0,vs=0)
67: (b4) w3 = 2 ; R3_w=2
68: (85) call bpf_arena_free_pages#72675 ;
69: (b7) r1 = 0 ; R1_w=0
; page[i + 1] = NULL; @ verifier_arena_large.c:243
70: (7b) *(u64 *)(r8 +8) = r1
R8 invalid mem access 'scalar'
processed 61 insns (limit 1000000) max_states_per_insn 0 total_states 6 peak_states 6 mark_read 2
=============
#489/5 verifier_arena_large/big_alloc2:FAIL
The main reason is that 'r8' in insn '70' is not an arena pointer.
Further debugging at llvm side shows that llvm commit ([1]) caused
the failure. For the original code:
page[i] = NULL;
page[i + 1] = NULL;
the llvm transformed it to something like below at source level:
__builtin_memset(&page[i], 0, 16)
Such transformation prevents llvm BPFCheckAndAdjustIR pass from
generating proper addr_space_cast insns ([2]).
Adding support in llvm BPFCheckAndAdjustIR pass should work, but
not sure that such a pattern exists or not in real applications.
At the same time, simply adding a memory barrier between two 'page'
assignment can fix the issue.
[1] https://github.com/llvm/llvm-project/pull/155415
[2] https://github.com/llvm/llvm-project/pull/84410
Cc: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20250920045805.3288551-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | tools/testing/selftests/bpf/progs/verifier_arena_large.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/progs/verifier_arena_large.c b/tools/testing/selftests/bpf/progs/verifier_arena_large.c index 9dbdf123542d..f19e15400b3e 100644 --- a/tools/testing/selftests/bpf/progs/verifier_arena_large.c +++ b/tools/testing/selftests/bpf/progs/verifier_arena_large.c @@ -240,6 +240,7 @@ int big_alloc2(void *ctx) return 5; bpf_arena_free_pages(&arena, (void __arena *)pg, 2); page[i] = NULL; + barrier(); page[i + 1] = NULL; cond_break; } |