On 11/3/2015 10:56 PM, Zi Shen Lim wrote:
In the case of division by zero in a BPF program:
A = A / X; (X == 0)
the expected behavior is to terminate with return value 0.
This is confirmed by the test case introduced in commit 86bf1721b226
("test_bpf: add tests checking that JIT/interpreter sets A and X to 0.").
Reported-by: Shi, Yang <yang.shi@xxxxxxxxxx>
Thanks for coming up with the fix promptly.
s/Shi, Yang/Yang Shi
Tested with the latest 4.3 kernel.
Tested-by: Yang Shi <yang.shi@xxxxxxxxxx>
Yang
CC: Xi Wang <xi.wang@xxxxxxxxx>
CC: Alexei Starovoitov <ast@xxxxxxxxxxxx>
CC: Catalin Marinas <catalin.marinas@xxxxxxx>
CC: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
Cc: <stable@xxxxxxxxxxxxxxx> # 3.18+
Signed-off-by: Zi Shen Lim <zlim.lnx@xxxxxxxxx>
---
arch/arm64/net/bpf_jit.h | 3 ++-
arch/arm64/net/bpf_jit_comp.c | 37 +++++++++++++++++++++++++------------
2 files changed, 27 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/net/bpf_jit.h b/arch/arm64/net/bpf_jit.h
index 98a26ce..aee5637 100644
--- a/arch/arm64/net/bpf_jit.h
+++ b/arch/arm64/net/bpf_jit.h
@@ -1,7 +1,7 @@
/*
* BPF JIT compiler for ARM64
*
- * Copyright (C) 2014 Zi Shen Lim <zlim.lnx@xxxxxxxxx>
+ * Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx@xxxxxxxxx>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
@@ -35,6 +35,7 @@
aarch64_insn_gen_comp_branch_imm(0, offset, Rt, A64_VARIANT(sf), \
AARCH64_INSN_BRANCH_COMP_##type)
#define A64_CBZ(sf, Rt, imm19) A64_COMP_BRANCH(sf, Rt, (imm19) << 2, ZERO)
+#define A64_CBNZ(sf, Rt, imm19) A64_COMP_BRANCH(sf, Rt, (imm19) << 2, NONZERO)
/* Conditional branch (immediate) */
#define A64_COND_BRANCH(cond, offset) \
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index c047598..9ae6f23 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1,7 +1,7 @@
/*
* BPF JIT compiler for ARM64
*
- * Copyright (C) 2014 Zi Shen Lim <zlim.lnx@xxxxxxxxx>
+ * Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx@xxxxxxxxx>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
@@ -225,6 +225,17 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
u8 jmp_cond;
s32 jmp_offset;
+#define check_imm(bits, imm) do { \
+ if ((((imm) > 0) && ((imm) >> (bits))) || \
+ (((imm) < 0) && (~(imm) >> (bits)))) { \
+ pr_info("[%2d] imm=%d(0x%x) out of range\n", \
+ i, imm, imm); \
+ return -EINVAL; \
+ } \
+} while (0)
+#define check_imm19(imm) check_imm(19, imm)
+#define check_imm26(imm) check_imm(26, imm)
+
switch (code) {
/* dst = src */
case BPF_ALU | BPF_MOV | BPF_X:
@@ -258,8 +269,21 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
break;
case BPF_ALU | BPF_DIV | BPF_X:
case BPF_ALU64 | BPF_DIV | BPF_X:
+ {
+ const u8 r0 = bpf2a64[BPF_REG_0];
+
+ /* if (src == 0) return 0 */
+ jmp_offset = 3; /* skip ahead to else path */
+ check_imm19(jmp_offset);
+ emit(A64_CBNZ(is64, src, jmp_offset), ctx);
+ emit(A64_MOVZ(1, r0, 0, 0), ctx);
+ jmp_offset = epilogue_offset(ctx);
+ check_imm26(jmp_offset);
+ emit(A64_B(jmp_offset), ctx);
+ /* else */
emit(A64_UDIV(is64, dst, dst, src), ctx);
break;
+ }
case BPF_ALU | BPF_MOD | BPF_X:
case BPF_ALU64 | BPF_MOD | BPF_X:
ctx->tmp_used = 1;
@@ -393,17 +417,6 @@ emit_bswap_uxt:
emit(A64_ASR(is64, dst, dst, imm), ctx);
break;
-#define check_imm(bits, imm) do { \
- if ((((imm) > 0) && ((imm) >> (bits))) || \
- (((imm) < 0) && (~(imm) >> (bits)))) { \
- pr_info("[%2d] imm=%d(0x%x) out of range\n", \
- i, imm, imm); \
- return -EINVAL; \
- } \
-} while (0)
-#define check_imm19(imm) check_imm(19, imm)
-#define check_imm26(imm) check_imm(26, imm)
-
/* JUMP off */
case BPF_JMP | BPF_JA:
jmp_offset = bpf2a64_offset(i + off, i, ctx);
--
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