From a1b14abc009d9c13be355dbd4a4c4d47816ad3db Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Tue, 22 Jan 2019 22:45:21 -0800 Subject: [PATCH] bpf: verifier: remove unconditional branches by 0 Unconditional branches by 0 instructions are basically noops but they can result from earlier optimizations, e.g. a conditional jumps which would never be taken or a conditional jump around dead code. Remove those branches. v0.2: - s/opt_remove_dead_branches/opt_remove_nops/ (Jiong). Signed-off-by: Jakub Kicinski Reviewed-by: Jiong Wang Acked-by: Yonghong Song Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 099b2541f87f..f39bca188a5c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6660,6 +6660,27 @@ static int opt_remove_dead_code(struct bpf_verifier_env *env) return 0; } +static int opt_remove_nops(struct bpf_verifier_env *env) +{ + const struct bpf_insn ja = BPF_JMP_IMM(BPF_JA, 0, 0, 0); + struct bpf_insn *insn = env->prog->insnsi; + int insn_cnt = env->prog->len; + int i, err; + + for (i = 0; i < insn_cnt; i++) { + if (memcmp(&insn[i], &ja, sizeof(ja))) + continue; + + err = verifier_remove_insns(env, i, 1); + if (err) + return err; + insn_cnt--; + i--; + } + + return 0; +} + /* convert load instructions that access fields of a context type into a * sequence of instructions that access fields of the underlying structure: * struct __sk_buff -> struct sk_buff @@ -7452,6 +7473,8 @@ skip_full_check: opt_hard_wire_dead_code_branches(env); if (ret == 0) ret = opt_remove_dead_code(env); + if (ret == 0) + ret = opt_remove_nops(env); } else { if (ret == 0) sanitize_dead_code(env);