linux-kernel - Re: [PATCH] arm64: bpf: fix div-by-zero case

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Message-ID: <CAKU6vyZu5KNAipSVUMg8ASnRXztVwh57weKXxXOXkqAJ3erDBQ@mail.gmail.com>
Date:	Tue, 3 Nov 2015 23:04:05 -0800
From:	Xi Wang <xi.wang@...il.com>
To:	Zi Shen Lim <zlim.lnx@...il.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64: bpf: fix div-by-zero case

On Tue, Nov 3, 2015 at 10:56 PM, Zi Shen Lim <zlim.lnx@...il.com> wrote:
>         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:

BPF_MOD might need the same fix.
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