diff options
| author | Yonghong Song <yhs@fb.com> | 2017-04-29 22:52:42 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-05-14 14:00:20 +0200 |
| commit | 7bca0a9702edfc8d0e7e46f984ca422ffdbe0498 (patch) | |
| tree | 0ba7e16e8d344286ab284b4c4e5cc83a3c81e46f | |
| parent | f3235cbd5be15aa084d5561c2eb8492ed68cd7e5 (diff) | |
bpf: enhance verifier to understand stack pointer arithmetic
[ Upstream commit 332270fdc8b6fba07d059a9ad44df9e1a2ad4529 ]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | kernel/bpf/verifier.c | 11 | ||||
| -rw-r--r-- | samples/bpf/test_verifier.c | 18 |
2 files changed, 23 insertions, 6 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7c9f94c53441..64fcab1d8cd9 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1749,6 +1749,17 @@ 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))) { diff --git a/samples/bpf/test_verifier.c b/samples/bpf/test_verifier.c index 369ffaad3799..dc7dec9e64ba 100644 --- a/samples/bpf/test_verifier.c +++ b/samples/bpf/test_verifier.c @@ -1218,16 +1218,22 @@ static struct bpf_test tests[] = { .result = ACCEPT, }, { - "unpriv: obfuscate stack pointer", + "stack pointer arithmetic", .insns = { - BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), - BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), - BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), + BPF_MOV64_IMM(BPF_REG_1, 4), + BPF_JMP_IMM(BPF_JA, 0, 0, 0), + BPF_MOV64_REG(BPF_REG_7, BPF_REG_10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -10), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_7, -10), + BPF_MOV64_REG(BPF_REG_2, BPF_REG_7), + BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1), + BPF_ST_MEM(0, BPF_REG_2, 4, 0), + BPF_MOV64_REG(BPF_REG_2, BPF_REG_7), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, 8), + BPF_ST_MEM(0, BPF_REG_2, 4, 0), BPF_MOV64_IMM(BPF_REG_0, 0), BPF_EXIT_INSN(), }, - .errstr_unpriv = "R2 pointer arithmetic", - .result_unpriv = REJECT, .result = ACCEPT, }, { |