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authorAlexei Starovoitov <ast@fb.com>2016-05-19 18:17:14 -0700
committerDavid S. Miller <davem@davemloft.net>2016-05-20 19:53:03 -0400
commit1b9b69ecb3a5236d4d3da0f0fa11af916371841e (patch)
tree1f5773cda4c0b535c4432f12a633ff304d11a004 /kernel/bpf
parentd91b28ed42de99217efb2e8cb0357263d6fb737c (diff)
downloadlinux-sh-1b9b69ecb3a5236d4d3da0f0fa11af916371841e.tar.gz
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/bpf')
-rw-r--r--kernel/bpf/verifier.c18
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 = &regs[insn->dst_reg];
struct reg_state *src_reg = &regs[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 &&