[PATCH 5.10.y] iommu/dma: Catch scatterlist length overflows

[Sasha Levin <sashal@kernel.org>]

From: Krzysztof Karas <krzysztof.karas@intel.com>

[ Upstream commit 1c8f6308e557f32412e9d4678b3f029f47f6d9aa ]

It is possible, when a very large mapping uses only one
scatterlist, that padding overflows scatterlist's length field.
This results in:
 1) silently wrapping the value
 2) smaller than desired mappings produced by iommu_map_sg
 3) leaving mapped bytes in memory (no iommu_unmap)

Address this issue by adding overflow detection for scatterlist
length field.

Fixes: 809eac54cdd6 ("iommu/dma: Implement scatterlist segment merging")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
[ sashal: adapted overflow handling to use an unsigned int cast comparison while preserving zero-on-failure returns ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iommu/dma-iommu.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 62dd195d88062..321c2f34de4dc 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -864,6 +864,8 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
 		sg_dma_len(s) = s_length;
 		s->offset -= s_iova_off;
 		s_length = iova_align(iovad, s_length + s_iova_off);
+		if (s_length != (unsigned int)s_length)
+			goto out_restore_sg;
 		s->length = s_length;
 
 		/*
@@ -880,7 +882,17 @@ static int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
 		 *   time through here (i.e. before it has a meaningful value).
 		 */
 		if (pad_len && pad_len < s_length - 1) {
-			prev->length += pad_len;
+			unsigned int new_prev_len;
+
+			/*
+			 * For large mappings spanning multiple GBs we
+			 * may not be able to fit all needed padding into
+			 * sg->length.
+			 */
+			if (check_add_overflow(prev->length, pad_len, &new_prev_len))
+				goto out_restore_sg;
+
+			prev->length = new_prev_len;
 			iova_len += pad_len;
 		}
 
-- 
2.53.0