Re: [PATCH 2/2] crypto: arm64/crct10dif - revert to C code for short inputs

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Jan 24, 2019 at 07:27:12PM +0100, Ard Biesheuvel wrote:
> The SIMD routine ported from x86 used to have a special code path
> for inputs < 16 bytes, which got lost somewhere along the way.
> Instead, the current glue code aligns the input pointer to permit
> the NEON routine to use special versions of the vld1 instructions
> that assume 16 byte alignment, but this could result in inputs of
> less than 16 bytes to be passed in. 

This description doesn't quite match the patch since the arm64 version of the
assembly doesn't use any alignment specifiers.  I take it that actually means
the alignment in the glue code wasn't necessary in the first place?

> This not only fails the new
> extended tests that Eric has implemented, it also results in the
> code reading before the input pointer, which could potentially
> result in crashes when dealing with less than 16 bytes of input
> at the start of a page which is preceded by an unmapped page.
> 
> So update the glue code to only invoke the NEON routine if the
> input is more than 16 bytes.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Can you add:

Fixes: 6ef5737f3931 ("crypto: arm64/crct10dif - port x86 SSE implementation to arm64")
Cc: stable@vger.kernel.org

> ---
>  arch/arm64/crypto/crct10dif-ce-glue.c | 25 +++++---------------
>  1 file changed, 6 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm64/crypto/crct10dif-ce-glue.c b/arch/arm64/crypto/crct10dif-ce-glue.c
> index b461d62023f2..567c24f3d224 100644
> --- a/arch/arm64/crypto/crct10dif-ce-glue.c
> +++ b/arch/arm64/crypto/crct10dif-ce-glue.c
> @@ -39,26 +39,13 @@ static int crct10dif_update(struct shash_desc *desc, const u8 *data,
>  			    unsigned int length)
>  {
>  	u16 *crc = shash_desc_ctx(desc);
> -	unsigned int l;
>  
> -	if (unlikely((u64)data % CRC_T10DIF_PMULL_CHUNK_SIZE)) {
> -		l = min_t(u32, length, CRC_T10DIF_PMULL_CHUNK_SIZE -
> -			  ((u64)data % CRC_T10DIF_PMULL_CHUNK_SIZE));
> -
> -		*crc = crc_t10dif_generic(*crc, data, l);
> -
> -		length -= l;
> -		data += l;
> -	}
> -
> -	if (length > 0) {
> -		if (may_use_simd()) {
> -			kernel_neon_begin();
> -			*crc = crc_t10dif_pmull(*crc, data, length);
> -			kernel_neon_end();
> -		} else {
> -			*crc = crc_t10dif_generic(*crc, data, length);
> -		}
> +	if (length >= CRC_T10DIF_PMULL_CHUNK_SIZE && may_use_simd()) {
> +		kernel_neon_begin();
> +		*crc = crc_t10dif_pmull(*crc, data, length);
> +		kernel_neon_end();
> +	} else {
> +		*crc = crc_t10dif_generic(*crc, data, length);
>  	}
>  
>  	return 0;
> -- 
> 2.17.1
>