diff options
| author | Alexei Starovoitov <ast@fb.com> | 2016-05-19 18:17:14 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-05-20 19:53:03 -0400 |
| commit | 1b9b69ecb3a5236d4d3da0f0fa11af916371841e (patch) | |
| tree | 1f5773cda4c0b535c4432f12a633ff304d11a004 /kernel | |
| parent | d91b28ed42de99217efb2e8cb0357263d6fb737c (diff) | |
| download | lwn-1b9b69ecb3a5236d4d3da0f0fa11af916371841e.tar.gz lwn-1b9b69ecb3a5236d4d3da0f0fa11af916371841e.zip | |
bpf: teach verifier to recognize imm += ptr pattern
Humans don't write C code like:
u8 *ptr = skb->data;
int imm = 4;
imm += ptr;
but from llvm backend point of view 'imm' and 'ptr' are registers and
imm += ptr may be preferred vs ptr += imm depending which register value
will be used further in the code, while verifier can only recognize ptr += imm.
That caused small unrelated changes in the C code of the bpf program to
trigger rejection by the verifier. Therefore teach the verifier to recognize
both ptr += imm and imm += ptr.
For example:
when R6=pkt(id=0,off=0,r=62) R7=imm22
after r7 += r6 instruction
will be R6=pkt(id=0,off=0,r=62) R7=pkt(id=0,off=22,r=62)
Fixes: 969bf05eb3ce ("bpf: direct packet access")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d54e34874579..668e07903c8f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1245,6 +1245,7 @@ static int check_packet_ptr_add(struct verifier_env *env, struct bpf_insn *insn) struct reg_state *regs = env->cur_state.regs; struct reg_state *dst_reg = ®s[insn->dst_reg]; struct reg_state *src_reg = ®s[insn->src_reg]; + struct reg_state tmp_reg; s32 imm; if (BPF_SRC(insn->code) == BPF_K) { @@ -1267,6 +1268,19 @@ add_imm: */ dst_reg->off += imm; } else { + if (src_reg->type == PTR_TO_PACKET) { + /* R6=pkt(id=0,off=0,r=62) R7=imm22; r7 += r6 */ + tmp_reg = *dst_reg; /* save r7 state */ + *dst_reg = *src_reg; /* copy pkt_ptr state r6 into r7 */ + src_reg = &tmp_reg; /* pretend it's src_reg state */ + /* if the checks below reject it, the copy won't matter, + * since we're rejecting the whole program. If all ok, + * then imm22 state will be added to r7 + * and r7 will be pkt(id=0,off=22,r=62) while + * r6 will stay as pkt(id=0,off=0,r=62) + */ + } + if (src_reg->type == CONST_IMM) { /* pkt_ptr += reg where reg is known constant */ imm = src_reg->imm; @@ -1565,7 +1579,9 @@ static int check_alu_op(struct 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_PACKET) { + (dst_reg->type == PTR_TO_PACKET || + (BPF_SRC(insn->code) == BPF_X && + regs[insn->src_reg].type == PTR_TO_PACKET))) { /* ptr_to_packet += K|X */ return check_packet_ptr_add(env, insn); } else if (BPF_CLASS(insn->code) == BPF_ALU64 && |