crypto: caam - use len instead of nents for bulding HW S/G table

Currently, conversion of SW S/G table into HW S/G layout relies on
nents returned by sg_nents_for_len(sg, len).
However this leaves the possibility of HW S/G referencing more data
then needed: since buffer length in HW S/G entries is filled using
sg_dma_len(sg), the last entry in HW S/G table might have a length
that is bigger than needed for the crypto request.

This way of S/G table conversion is fine, unless after converting a table
more entries have to be appended to the HW S/G table.
In this case, crypto engine would access data from the S/G entry having
the incorrect length, instead of advancing in the S/G table.
This situation doesn't exist, but the upcoming implementation of
IV update for skcipher algorithms needs to add a S/G entry after
req->dst S/G (corresponding to output IV).

Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/caam/caamhash.c

@@ -729,7 +729,7 @@ static int ahash_edesc_add_src(struct caam_hash_ctx *ctx,
 		unsigned int sgsize = sizeof(*sg) *
 				      pad_sg_nents(first_sg + nents);
 
-		sg_to_sec4_sg_last(req->src, nents, sg + first_sg, 0);
+		sg_to_sec4_sg_last(req->src, to_hash, sg + first_sg, 0);
 
 		src_dma = dma_map_single(ctx->jrdev, sg, sgsize, DMA_TO_DEVICE);
 		if (dma_mapping_error(ctx->jrdev, src_dma)) {
@@ -788,9 +788,9 @@ static int ahash_update_ctx(struct ahash_request *req)
 
 	if (to_hash) {
 		int pad_nents;
+		int src_len = req->nbytes - *next_buflen;
 
-		src_nents = sg_nents_for_len(req->src,
-					     req->nbytes - (*next_buflen));
+		src_nents = sg_nents_for_len(req->src, src_len);
 		if (src_nents < 0) {
 			dev_err(jrdev, "Invalid number of src SG.\n");
 			return src_nents;
@@ -835,7 +835,7 @@ static int ahash_update_ctx(struct ahash_request *req)
 			goto unmap_ctx;
 
 		if (mapped_nents)
-			sg_to_sec4_sg_last(req->src, mapped_nents,
+			sg_to_sec4_sg_last(req->src, src_len,
 					   edesc->sec4_sg + sec4_sg_src_index,
 					   0);
 		else
@@ -1208,9 +1208,9 @@ static int ahash_update_no_ctx(struct ahash_request *req)
 
 	if (to_hash) {
 		int pad_nents;
+		int src_len = req->nbytes - *next_buflen;
 
-		src_nents = sg_nents_for_len(req->src,
-					     req->nbytes - *next_buflen);
+		src_nents = sg_nents_for_len(req->src, src_len);
 		if (src_nents < 0) {
 			dev_err(jrdev, "Invalid number of src SG.\n");
 			return src_nents;
@@ -1250,8 +1250,7 @@ static int ahash_update_no_ctx(struct ahash_request *req)
 		if (ret)
 			goto unmap_ctx;
 
-		sg_to_sec4_sg_last(req->src, mapped_nents,
-				   edesc->sec4_sg + 1, 0);
+		sg_to_sec4_sg_last(req->src, src_len, edesc->sec4_sg + 1, 0);
 
 		if (*next_buflen) {
 			scatterwalk_map_and_copy(next_buf, req->src,