[PATCH] arm64: bpf: fix div-by-zero case
Shi, Yang
yang.shi at linaro.org
Wed Nov 4 10:03:21 PST 2015
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 at linaro.org>
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 at linaro.org>
Yang
> CC: Xi Wang <xi.wang at gmail.com>
> CC: Alexei Starovoitov <ast at plumgrid.com>
> CC: Catalin Marinas <catalin.marinas at arm.com>
> CC: linux-arm-kernel at lists.infradead.org
> CC: linux-kernel at vger.kernel.org
> Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
> Cc: <stable at vger.kernel.org> # 3.18+
> Signed-off-by: Zi Shen Lim <zlim.lnx at gmail.com>
> ---
> 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 at gmail.com>
> + * Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx at gmail.com>
> *
> * 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 at gmail.com>
> + * Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx at gmail.com>
> *
> * 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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