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Subject: Re: [PATCH bpf] bpf: fix BPF_ALU32 | BPF_ARSH on BE arches
To:     Jiong Wang <jiong.wang@netronome.com>, alexei.starovoitov@gmail.com
Cc:     yauheni.kaliuta@redhat.com, bpf@vger.kernel.org,
        netdev@vger.kernel.org, oss-drivers@netronome.com
References: <1561480910-23543-1-git-send-email-jiong.wang@netronome.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
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Date:   Wed, 26 Jun 2019 16:31:43 +0200
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On 06/25/2019 06:41 PM, Jiong Wang wrote:
> Yauheni reported the following code do not work correctly on BE arches:
> 
>        ALU_ARSH_X:
>                DST = (u64) (u32) ((*(s32 *) &DST) >> SRC);
>                CONT;
>        ALU_ARSH_K:
>                DST = (u64) (u32) ((*(s32 *) &DST) >> IMM);
>                CONT;
> 
> and are causing failure of test_verifier test 'arsh32 on imm 2' on BE
> arches.
> 
> The code is taking address and interpreting memory directly, so is not
> endianness neutral. We should instead perform standard C type casting on
> the variable. A u64 to s32 conversion will drop the high 32-bit and reserve
> the low 32-bit as signed integer, this is all we want.
> 
> Fixes: 2dc6b100f928 ("bpf: interpreter support BPF_ALU | BPF_ARSH")
> Reported-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
> Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
> Signed-off-by: Jiong Wang <jiong.wang@netronome.com>

Applied, thanks!