linux-kernel - Re: [PATCH] powerpc: fix csum_ipv6_magic() on little endian platforms

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Date:   Mon, 10 Sep 2018 22:28:08 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     benh@...nel.crashing.org, paulus@...ba.org,
        Michael Ellerman <mpe@...erman.id.au>, jishi@...hat.com,
        LKML <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org, stable@...r.kernel.org
Subject: Re: [PATCH] powerpc: fix csum_ipv6_magic() on little endian platforms

On Mon, Sep 10, 2018 at 2:09 PM Christophe Leroy
<christophe.leroy@....fr> wrote:
>
> On little endian platforms, csum_ipv6_magic() keeps len and proto in
> CPU byte order. This generates a bad results leading to ICMPv6 packets
> from other hosts being dropped by powerpc64le platforms.
>
> In order to fix this, len and proto should be converted to network
> byte order ie bigendian byte order. However checksumming 0x12345678
> and 0x56341278 provide the exact same result so it is enough to
> rotate the sum of len and proto by 1 byte.
>
> PPC32 only support bigendian so the fix is needed for PPC64 only
>
> Fixes: e9c4943a107b ("powerpc: Implement csum_ipv6_magic in assembly")
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Reported-by: Xin Long <lucien.xin@...il.com>
> Cc: <stable@...r.kernel.org> # 4.18+
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/lib/checksum_64.S | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/powerpc/lib/checksum_64.S b/arch/powerpc/lib/checksum_64.S
> index 886ed94b9c13..2a68c43e13f5 100644
> --- a/arch/powerpc/lib/checksum_64.S
> +++ b/arch/powerpc/lib/checksum_64.S
> @@ -443,6 +443,9 @@ _GLOBAL(csum_ipv6_magic)
>         addc    r0, r8, r9
>         ld      r10, 0(r4)
>         ld      r11, 8(r4)
> +#ifndef CONFIG_CPU_BIG_ENDIAN
> +       rotldi  r5, r5, 8
> +#endif
>         adde    r0, r0, r10
>         add     r5, r5, r7
>         adde    r0, r0, r11
> --
> 2.13.3
>
Tested-by: Xin Long <lucien.xin@...il.com>