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authorYonghong Song <yhs@fb.com>2017-04-29 22:52:42 -0700
committerDavid S. Miller <davem@davemloft.net>2017-05-01 11:40:23 -0400
commit332270fdc8b6fba07d059a9ad44df9e1a2ad4529 (patch)
tree95e4cf412f1691c5ac9063c64989337fc80a278e /kernel/bpf/verifier.c
parent2faf26575350e49c1e242b7a464e9302f78b9b15 (diff)
bpf: enhance verifier to understand stack pointer arithmetic
llvm 4.0 and above generates the code like below: .... 440: (b7) r1 = 15 441: (05) goto pc+73 515: (79) r6 = *(u64 *)(r10 -152) 516: (bf) r7 = r10 517: (07) r7 += -112 518: (bf) r2 = r7 519: (0f) r2 += r1 520: (71) r1 = *(u8 *)(r8 +0) 521: (73) *(u8 *)(r2 +45) = r1 .... and the verifier complains "R2 invalid mem access 'inv'" for insn #521. This is because verifier marks register r2 as unknown value after #519 where r2 is a stack pointer and r1 holds a constant value. Teach verifier to recognize "stack_ptr + imm" and "stack_ptr + reg with const val" as valid stack_ptr with new offset. Signed-off-by: Yonghong Song <yhs@fb.com> Acked-by: Martin KaFai Lau <kafai@fb.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/bpf/verifier.c')
-rw-r--r--kernel/bpf/verifier.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6f8b6ed690be..c2ff608c1984 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1924,6 +1924,17 @@ static int check_alu_op(struct bpf_verifier_env *env, struct bpf_insn *insn)
return 0;
} else if (opcode == BPF_ADD &&
BPF_CLASS(insn->code) == BPF_ALU64 &&
+ dst_reg->type == PTR_TO_STACK &&
+ ((BPF_SRC(insn->code) == BPF_X &&
+ regs[insn->src_reg].type == CONST_IMM) ||
+ BPF_SRC(insn->code) == BPF_K)) {
+ if (BPF_SRC(insn->code) == BPF_X)
+ dst_reg->imm += regs[insn->src_reg].imm;
+ else
+ dst_reg->imm += insn->imm;
+ return 0;
+ } else if (opcode == BPF_ADD &&
+ BPF_CLASS(insn->code) == BPF_ALU64 &&
(dst_reg->type == PTR_TO_PACKET ||
(BPF_SRC(insn->code) == BPF_X &&
regs[insn->src_reg].type == PTR_TO_PACKET))) {