On Tue, 2016-08-02 at 10:07 +0200, Christophe Leroy wrote:
> commit 7aef4136566b0 ("powerpc32: rewrite csum_partial_copy_generic()
> based on copy_tofrom_user()") introduced a bug when destination
> address is odd and initial csum is not null
> 
> In that (rare) case the initial csum value has to be rotated one byte
> as well as the resulting value is
> 
> This patch also fixes related comments
> 
> Fixes: 7aef4136566b0 ("powerpc32: rewrite csum_partial_copy_generic()
> based on copy_tofrom_user()")
> Cc: sta...@vger.kernel.org
> 
> Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr>
> ---
>  v2: updated comments as suggested by Segher
> 
>  arch/powerpc/lib/checksum_32.S | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Alessio, can you confirm whether this fixes the problem you reported?

-Scott

> 
> diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S
> index d90870a..0a57fe6 100644
> --- a/arch/powerpc/lib/checksum_32.S
> +++ b/arch/powerpc/lib/checksum_32.S
> @@ -127,8 +127,9 @@ _GLOBAL(csum_partial_copy_generic)
>       stw     r7,12(r1)
>       stw     r8,8(r1)
>  
> -     andi.   r0,r4,1                 /* is destination
> address even ? */
> -     cmplwi  cr7,r0,0
> +     rlwinm  r0,r4,3,0x8
> +     rlwnm   r6,r6,r0,0,31   /* odd destination address:
> rotate one byte */
> +     cmplwi  cr7,r0,0        /* is destination address even ? */
>       addic   r12,r6,0
>       addi    r6,r4,-4
>       neg     r0,r4
> @@ -237,7 +238,7 @@ _GLOBAL(csum_partial_copy_generic)
>  66:  addze   r3,r12
>       addi    r1,r1,16
>       beqlr+  cr7
> -     rlwinm  r3,r3,8,0,31    /* swap bytes for odd destination
> */
> +     rlwinm  r3,r3,8,0,31    /* odd destination address:
> rotate one byte */
>       blr
>  
>  /* read fault */

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