Re: [PATCH v3 2/6] drivers: crypto: qce: sha: Hold back a block of data to be transferred as part of final

Bjorn Andersson
2021-01-26T07:46:57Z

On Wed 20 Jan 12:48 CST 2021, Thara Gopinath wrote:

> If the available data to transfer is exactly a multiple of block size, save
> the last block to be transferred in qce_ahash_final (with the last block
> bit set) if this is indeed the end of data stream. If not this saved block
> will be transferred as part of next update. If this block is not held back
> and if this is indeed the end of data stream, the digest obtained will be
> wrong since qce_ahash_final will see that rctx->buflen is 0 and return
> doing nothing which in turn means that a digest will not be copied to the
> destination result buffer. qce_ahash_final cannot be made to alter this
> behavior and allowed to proceed if rctx->buflen is 0 because the crypto
> engine BAM does not allow for zero length transfers.
>

Please drop "drivers: " from $subject.

Apart from that this looks good.

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Regards,
Bjorn

> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
> drivers/crypto/qce/sha.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/drivers/crypto/qce/sha.c b/drivers/crypto/qce/sha.c
> index 08aed03e2b59..dd263c5e4dd8 100644
> --- a/drivers/crypto/qce/sha.c
> +++ b/drivers/crypto/qce/sha.c
> @@ -216,6 +216,25 @@ static int qce_ahash_update(struct ahash_request *req)
>
> /* calculate how many bytes will be hashed later */
> hash_later = total % blocksize;
> +
> + /*
> + * At this point, there is more than one block size of data. If
> + * the available data to transfer is exactly a multiple of block
> + * size, save the last block to be transferred in qce_ahash_final
> + * (with the last block bit set) if this is indeed the end of data
> + * stream. If not this saved block will be transferred as part of
> + * next update. If this block is not held back and if this is
> + * indeed the end of data stream, the digest obtained will be wrong
> + * since qce_ahash_final will see that rctx->buflen is 0 and return
> + * doing nothing which in turn means that a digest will not be
> + * copied to the destination result buffer. qce_ahash_final cannot
> + * be made to alter this behavior and allowed to proceed if
> + * rctx->buflen is 0 because the crypto engine BAM does not allow
> + * for zero length transfers.
> + */
> + if (!hash_later)
> + hash_later = blocksize;
> +
> if (hash_later) {
> unsigned int src_offset = req->nbytes - hash_later;
> scatterwalk_map_and_copy(rctx->buf, req->src, src_offset,
> --
> 2.25.1
>