From mboxrd@z Thu Jan 1 00:00:00 1970 From: yang.shi@linaro.org (Shi, Yang) Date: Wed, 04 Nov 2015 10:03:21 -0800 Subject: [PATCH] arm64: bpf: fix div-by-zero case In-Reply-To: <1446620204-4228-1-git-send-email-zlim.lnx@gmail.com> References: <1446620204-4228-1-git-send-email-zlim.lnx@gmail.com> Message-ID: <563A4869.1000902@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 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 > CC: Xi Wang > CC: Alexei Starovoitov > CC: Catalin Marinas > CC: linux-arm-kernel at lists.infradead.org > CC: linux-kernel at vger.kernel.org > Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler") > Cc: # 3.18+ > Signed-off-by: Zi Shen Lim > --- > 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 > + * Copyright (C) 2014-2015 Zi Shen Lim > * > * 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 > + * Copyright (C) 2014-2015 Zi Shen Lim > * > * 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); >