crypto: ccree - protect against empty or NULL scatterlists

Deal gracefully with a NULL or empty scatterlist which can happen
if both cryptlen and assoclen are zero and we're doing in-place
AEAD encryption.

This fixes a crash when this causes us to try and map a NULL page,
at least with some platforms / DMA mapping configs.

Cc: [e-mail] # v4.19+
Reported-by: Geert Uytterhoeven <[e-mail]>
Tested-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Gilad Ben-Yossef <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

drivers/crypto/ccree/cc_buffer_mgr.c

···
 {
 	unsigned int nents = 0;
 
+	*lbytes = 0;
+
 	while (nbytes && sg_list) {
 		nents++;
 		/* get the number of bytes in the last entry */
···
 				nbytes : sg_list->length;
 		sg_list = sg_next(sg_list);
 	}
+
 	dev_dbg(dev, "nents %d last bytes %d\n", nents, *lbytes);
 	return nents;
 }
···
 		     unsigned int nbytes, int direction, u32 *nents,
 		     u32 max_sg_nents, u32 *lbytes, u32 *mapped_nents)
 {
-	if (sg_is_last(sg)) {
-		/* One entry only case -set to DLLI */
-		if (dma_map_sg(dev, sg, 1, direction) != 1) {
-			dev_err(dev, "dma_map_sg() single buffer failed\n");
-			return -ENOMEM;
-		}
-		dev_dbg(dev, "Mapped sg: dma_address=%pad page=%p addr=%pK offset=%u length=%u\n",
-			&sg_dma_address(sg), sg_page(sg), sg_virt(sg),
-			sg->offset, sg->length);
-		*lbytes = nbytes;
-		*nents = 1;
-		*mapped_nents = 1;
-	} else {  /*sg_is_last*/
-		*nents = cc_get_sgl_nents(dev, sg, nbytes, lbytes);
-		if (*nents > max_sg_nents) {
-			*nents = 0;
-			dev_err(dev, "Too many fragments. current %d max %d\n",
-				*nents, max_sg_nents);
-			return -ENOMEM;
-		}
-		/* In case of mmu the number of mapped nents might
-		 * be changed from the original sgl nents
-		 */
-		*mapped_nents = dma_map_sg(dev, sg, *nents, direction);
-		if (*mapped_nents == 0) {
-			*nents = 0;
-			dev_err(dev, "dma_map_sg() sg buffer failed\n");
-			return -ENOMEM;
-		}
+	int ret = 0;
+
+	*nents = cc_get_sgl_nents(dev, sg, nbytes, lbytes);
+	if (*nents > max_sg_nents) {
+		*nents = 0;
+		dev_err(dev, "Too many fragments. current %d max %d\n",
+			*nents, max_sg_nents);
+		return -ENOMEM;
 	}
+
+	ret = dma_map_sg(dev, sg, *nents, direction);
+	if (dma_mapping_error(dev, ret)) {
+		*nents = 0;
+		dev_err(dev, "dma_map_sg() sg buffer failed %d\n", ret);
+		return -ENOMEM;
+	}
+
+	*mapped_nents = ret;
 
 	return 0;
 }
···
 		sg_virt(req->src), areq_ctx->src.nents, areq_ctx->assoc.nents,
 		areq_ctx->assoclen, req->cryptlen);
 
-	dma_unmap_sg(dev, req->src, sg_nents(req->src), DMA_BIDIRECTIONAL);
+	dma_unmap_sg(dev, req->src, areq_ctx->src.mapped_nents,
+		     DMA_BIDIRECTIONAL);
 	if (req->src != req->dst) {
 		dev_dbg(dev, "Unmapping dst sgl: req->dst=%pK\n",
 			sg_virt(req->dst));
-		dma_unmap_sg(dev, req->dst, sg_nents(req->dst),
+		dma_unmap_sg(dev, req->dst, areq_ctx->dst.mapped_nents,
 			     DMA_BIDIRECTIONAL);
 	}
 	if (drvdata->coherent &&
···
 					    &src_last_bytes);
 	sg_index = areq_ctx->src_sgl->length;
 	//check where the data starts
-	while (sg_index <= size_to_skip) {
+	while (src_mapped_nents && (sg_index <= size_to_skip)) {
 		src_mapped_nents--;
 		offset -= areq_ctx->src_sgl->length;
 		sgl = sg_next(areq_ctx->src_sgl);
···
 			size_for_map += crypto_aead_ivsize(tfm);
 
 		rc = cc_map_sg(dev, req->dst, size_for_map, DMA_BIDIRECTIONAL,
-			       &areq_ctx->dst.nents,
+			       &areq_ctx->dst.mapped_nents,
 			       LLI_MAX_NUM_OF_DATA_ENTRIES, &dst_last_bytes,
 			       &dst_mapped_nents);
 		if (rc)
···
 	offset = size_to_skip;
 
 	//check where the data starts
-	while (sg_index <= size_to_skip) {
+	while (dst_mapped_nents && sg_index <= size_to_skip) {
 		dst_mapped_nents--;
 		offset -= areq_ctx->dst_sgl->length;
 		sgl = sg_next(areq_ctx->dst_sgl);
···
 	if (is_gcm4543)
 		size_to_map += crypto_aead_ivsize(tfm);
 	rc = cc_map_sg(dev, req->src, size_to_map, DMA_BIDIRECTIONAL,
-		       &areq_ctx->src.nents,
+		       &areq_ctx->src.mapped_nents,
 		       (LLI_MAX_NUM_OF_ASSOC_DATA_ENTRIES +
 			LLI_MAX_NUM_OF_DATA_ENTRIES),
 		       &dummy, &mapped_nents);

drivers/crypto/ccree/cc_buffer_mgr.h

···
 
 struct cc_mlli {
 	cc_sram_addr_t sram_addr;
+	unsigned int mapped_nents;
 	unsigned int nents; //sg nents
 	unsigned int mlli_nents; //mlli nents might be different than the above
 };