From 577c06af8188d1f6919ef7b62fc1b78fb1b86eb7 Mon Sep 17 00:00:00 2001 From: Ilya Leoshkevich Date: Tue, 19 Sep 2023 12:09:03 +0200 Subject: [PATCH] bpf: Disable zero-extension for BPF_MEMSX On the architectures that use bpf_jit_needs_zext(), e.g., s390x, the verifier incorrectly inserts a zero-extension after BPF_MEMSX, leading to miscompilations like the one below: 24: 89 1a ff fe 00 00 00 00 "r1 = *(s16 *)(r10 - 2);" # zext_dst set 0x3ff7fdb910e: lgh %r2,-2(%r13,%r0) # load halfword 0x3ff7fdb9114: llgfr %r2,%r2 # wrong! 25: 65 10 00 03 00 00 7f ff if r1 s> 32767 goto +3 # check_cond_jmp_op() Disable such zero-extensions. The JITs need to insert sign-extension themselves, if necessary. Suggested-by: Puranjay Mohan Signed-off-by: Ilya Leoshkevich Reviewed-by: Puranjay Mohan Link: https://lore.kernel.org/r/20230919101336.2223655-2-iii@linux.ibm.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 38f8718f1602..eed7350e15f4 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3114,7 +3114,7 @@ static bool is_reg64(struct bpf_verifier_env *env, struct bpf_insn *insn, if (class == BPF_LDX) { if (t != SRC_OP) - return BPF_SIZE(code) == BPF_DW; + return BPF_SIZE(code) == BPF_DW || BPF_MODE(code) == BPF_MEMSX; /* LDX source must be ptr. */ return true; } -- 2.25.1