From 3bf15921c58df982f9b15d64754c483785bf66f3 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 30 Nov 2017 21:31:39 -0800 Subject: [PATCH] bpf: improve JEQ/JNE path walking verifier knows how to trim paths that are known not to be taken at run-time when register containing run-time constant is compared with another constant. It was done only for JEQ comparison. Extend it to include JNE as well. More cases can be added in the future. before after bpf_lb-DLB_L3.o 2270 2051 bpf_lb-DLB_L4.o 3682 3287 bpf_lb-DUNKNOWN.o 1110 1080 bpf_lxc-DDROP_ALL.o 27876 24980 bpf_lxc-DUNKNOWN.o 38780 34308 bpf_netdev.o 16937 15404 bpf_overlay.o 7929 7191 Signed-off-by: Alexei Starovoitov Acked-by: John Fastabend Acked-by: Daniel Borkmann Signed-off-by: Daniel Borkmann --- kernel/bpf/verifier.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 46ff4e5b3fb7..afe9a1a0a5fe 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2955,8 +2955,9 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, if (BPF_SRC(insn->code) == BPF_K && (opcode == BPF_JEQ || opcode == BPF_JNE) && dst_reg->type == SCALAR_VALUE && - tnum_equals_const(dst_reg->var_off, insn->imm)) { - if (opcode == BPF_JEQ) { + tnum_is_const(dst_reg->var_off)) { + if ((opcode == BPF_JEQ && dst_reg->var_off.value == insn->imm) || + (opcode == BPF_JNE && dst_reg->var_off.value != insn->imm)) { /* if (imm == imm) goto pc+off; * only follow the goto, ignore fall-through */