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arm64: bpf: fix div-by-zero case 

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 86bf1721b2
("test_bpf: add tests checking that JIT/interpreter sets A and X to 0.").

Reported-by: Yang Shi <yang.shi@linaro.org>
Tested-by: Yang Shi <yang.shi@linaro.org>
CC: Xi Wang <xi.wang@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: linux-arm-kernel@lists.infradead.org
CC: linux-kernel@vger.kernel.org
Fixes: e54bcde3d6 ("arm64: eBPF JIT compiler")
Cc: <stable@vger.kernel.org> # 3.18+
Signed-off-by: Zi Shen Lim <zlim.lnx@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Zi Shen Lim 2015-11-03 22:56:44 -08:00 committed by Catalin Marinas
parent 4d17da4ca7
commit 251599e1d6
2 changed files with 27 additions and 13 deletions
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3
arch/arm64/net/bpf_jit.h
View File

@ -1,7 +1,7 @@
/*
* BPF JIT compiler for ARM64
*
* Copyright (C) 2014 Zi Shen Lim <zlim.lnx@gmail.com>
* Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx@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) \

37
arch/arm64/net/bpf_jit_comp.c
View File

@ -1,7 +1,7 @@
/*
* BPF JIT compiler for ARM64
*
* Copyright (C) 2014 Zi Shen Lim <zlim.lnx@gmail.com>
* Copyright (C) 2014-2015 Zi Shen Lim <zlim.lnx@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);