From: Alexei Starovoitov <ast@fb•com>
To: "David S . Miller" <davem@davemloft•net>
Cc: Daniel Borkmann <daniel@iogearbox•net>, <netdev@vger•kernel.org>,
<kernel-team@fb•com>
Subject: [PATCH net-next] bpf: enhance verifier to understand stack pointer arithmetic
Date: Sat, 29 Apr 2017 22:52:42 -0700 [thread overview]
Message-ID: <20170430055242.2536070-1-ast@fb.com> (raw)
From: Yonghong Song <yhs@fb•com>
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>
---
technically it's 'net' material, but it's too late for 'net',
hence 'net-next' tag.
No 'Fixes' tag, since it's only seen with newer llvm.
---
kernel/bpf/verifier.c | 11 +++++++++++
tools/testing/selftests/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 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))) {
diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 95a8d5f3ab80..0ea89456d478 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -1814,16 +1814,22 @@ 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,
},
{
--
2.9.3
next reply other threads:[~2017-04-30 5:52 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-30 5:52 Alexei Starovoitov [this message]
2017-05-01 2:57 ` [PATCH net-next] bpf: enhance verifier to understand stack pointer arithmetic David Miller
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