iommu: Do more input validation in iommu_map_sg()

The IOMMU-API works on page boundarys, unlike the DMA-API
which can work with sub-page buffers. The sg->offset
field does not make sense on the IOMMU level, so force it to
be 0. Do some error-path consolidation while at it.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -1127,26 +1127,33 @@ EXPORT_SYMBOL_GPL(iommu_unmap);
 size_t default_iommu_map_sg(struct iommu_domain *domain, unsigned long iova,
 			 struct scatterlist *sg, unsigned int nents, int prot)
 {
-	int ret;
+	struct scatterlist *s;
 	size_t mapped = 0;
 	unsigned int i;
-	struct scatterlist *s;
+	int ret;
 
 	for_each_sg(sg, s, nents, i) {
 		phys_addr_t phys = page_to_phys(sg_page(s));
-		size_t page_len = s->offset + s->length;
 
-		ret = iommu_map(domain, iova + mapped, phys, page_len, prot);
-		if (ret) {
-			/* undo mappings already done */
-			iommu_unmap(domain, iova, mapped);
-			mapped = 0;
-			break;
-		}
-		mapped += page_len;
+		/* We are mapping on page boundarys, so offset must be 0 */
+		if (s->offset)
+			goto out_err;
+
+		ret = iommu_map(domain, iova + mapped, phys, s->length, prot);
+		if (ret)
+			goto out_err;
+
+		mapped += s->length;
 	}
 
 	return mapped;
+
+out_err:
+	/* undo mappings already done */
+	iommu_unmap(domain, iova, mapped);
+
+	return 0;
+
 }
 EXPORT_SYMBOL_GPL(default_iommu_map_sg);