diff options
| -rw-r--r-- | kernel/bpf/verifier.c | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index dfb138b46488..8365259a7c5a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5064,14 +5064,21 @@ static struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 of return new_prog; } -/* The verifier does more data flow analysis than llvm and will not explore - * branches that are dead at run time. Malicious programs can have dead code - * too. Therefore replace all dead at-run-time code with nops. +/* The verifier does more data flow analysis than llvm and will not + * explore branches that are dead at run time. Malicious programs can + * have dead code too. Therefore replace all dead at-run-time code + * with 'ja -1'. + * + * Just nops are not optimal, e.g. if they would sit at the end of the + * program and through another bug we would manage to jump there, then + * we'd execute beyond program memory otherwise. Returning exception + * code also wouldn't work since we can have subprogs where the dead + * code could be located. */ static void sanitize_dead_code(struct bpf_verifier_env *env) { struct bpf_insn_aux_data *aux_data = env->insn_aux_data; - struct bpf_insn nop = BPF_MOV64_REG(BPF_REG_0, BPF_REG_0); + struct bpf_insn trap = BPF_JMP_IMM(BPF_JA, 0, 0, -1); struct bpf_insn *insn = env->prog->insnsi; const int insn_cnt = env->prog->len; int i; @@ -5079,7 +5086,7 @@ static void sanitize_dead_code(struct bpf_verifier_env *env) for (i = 0; i < insn_cnt; i++) { if (aux_data[i].seen) continue; - memcpy(insn + i, &nop, sizeof(nop)); + memcpy(insn + i, &trap, sizeof(trap)); } } |