From: Ilya Leoshkevich iii@linux.ibm.com
[ Upstream commit 45c709f8c71b525b51988e782febe84ce933e7e0 ]
"access skb fields ok" verifier test fails on s390 with the "verifier bug. zext_dst is set, but no reg is defined" message. The first insns of the test prog are ...
0: 61 01 00 00 00 00 00 00 ldxw %r0,[%r1+0] 8: 35 00 00 01 00 00 00 00 jge %r0,0,1 10: 61 01 00 08 00 00 00 00 ldxw %r0,[%r1+8]
... and the 3rd one is dead (this does not look intentional to me, but this is a separate topic).
sanitize_dead_code() converts dead insns into "ja -1", but keeps zext_dst. When opt_subreg_zext_lo32_rnd_hi32() tries to parse such an insn, it sees this discrepancy and bails. This problem can be seen only with JITs whose bpf_jit_needs_zext() returns true.
Fix by clearning dead insns' zext_dst.
The commits that contributed to this problem are:
1. 5aa5bd14c5f8 ("bpf: add initial suite for selftests"), which introduced the test with the dead code. 2. 5327ed3d44b7 ("bpf: verifier: mark verified-insn with sub-register zext flag"), which introduced the zext_dst flag. 3. 83a2881903f3 ("bpf: Account for BPF_FETCH in insn_has_def32()"), which introduced the sanity check. 4. 9183671af6db ("bpf: Fix leakage under speculation on mispredicted branches"), which bisect points to.
It's best to fix this on stable branches that contain the second one, since that's the point where the inconsistency was introduced.
Fixes: 5327ed3d44b7 ("bpf: verifier: mark verified-insn with sub-register zext flag") Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Link: https://lore.kernel.org/bpf/20210812151811.184086-2-iii@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ce1e9193365f..1410f128c404 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10705,6 +10705,7 @@ static void sanitize_dead_code(struct bpf_verifier_env *env) if (aux_data[i].seen) continue; memcpy(insn + i, &trap, sizeof(trap)); + aux_data[i].zext_dst = false; } }