linux-kernel - Re: [PATCH] lib/mpi: Fix kernel unaligned acces in mpi_write_to

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Message-ID: <57190C88.8000608@intel.com>
Date:	Thu, 21 Apr 2016 10:23:20 -0700
From:	Tadeusz Struk <tadeusz.struk@...el.com>
To:	Sowmini Varadhan <sowmini.varadhan@...cle.com>,
	linux-kernel@...r.kernel.org
Cc:	herbert@...dor.apana.org.au, smueller@...onox.de, mmarek@...e.com,
	arnd@...db.de, andrew.zaborowski@...el.com
Subject: Re: [PATCH] lib/mpi: Fix kernel unaligned acces in mpi_write_to_sgl

On 04/21/2016 04:07 AM, Sowmini Varadhan wrote:
> 
> Commit 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers") added
> mpi_write_to_sgl() which generates traps due to unaligned
> access on some platforms like sparc. Fix this by using
> the get_unaligned* and put_unaligned* functions.
> 
> Fixes: 2d4d1eea540b ("lib/mpi: Add mpi sgl helpers")
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> ---
>  lib/mpi/mpicoder.c |   12 ++++++++----
>  1 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/mpi/mpicoder.c b/lib/mpi/mpicoder.c
> index eb15e7d..6771378 100644
> --- a/lib/mpi/mpicoder.c
> +++ b/lib/mpi/mpicoder.c
> @@ -21,6 +21,7 @@
>  #include <linux/bitops.h>
>  #include <linux/count_zeros.h>
>  #include "mpi-internal.h"
> +#include <asm/unaligned.h>
>  
>  #define MAX_EXTERN_MPI_BITS 16384
>  
> @@ -405,10 +406,13 @@ int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
>  				p -= sizeof(alimb);
>  				continue;
>  			} else {
> -				mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
> -				mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
> -							+ lzeros;
> -				*limb1 = *limb2;
> +				mpi_limb_t tmp;
> +
> +				tmp = get_unaligned_be32((void *)p -
> +							 sizeof(alimb) +
> +							 lzeros);
> +				put_unaligned_be32(tmp,
> +						   (void *)p - sizeof(alimb));
>  				p -= lzeros;
>  				y = lzeros;
>  			}

What if the mpi_limb_t will happen to be 64 bit? 
Thanks,
-- 
TS