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")
Signed-off-by: Krzysztof Karas <[email protected]>
Reviewed-by: Robin Murphy <[email protected]>
---
v4:
* Added value wrap check before s->length assignment (Robin);
drivers/iommu/dma-iommu.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 381b60d9e7ce..3ca3196a41b0 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -21,6 +21,7 @@
#include <linux/iommu-dma.h>
#include <linux/iova.h>
#include <linux/irq.h>
+#include <linux/limits.h>
#include <linux/list_sort.h>
#include <linux/memremap.h>
#include <linux/mm.h>
@@ -1477,6 +1478,12 @@ int iommu_dma_map_sg(struct device *dev, struct
scatterlist *sg, int nents,
sg_dma_len(s) = s_length;
s->offset -= s_iova_off;
s_length = iova_align(iovad, s_length + s_iova_off);
+ if ((s_length & UINT_MAX) == 0) {
+ /* Prevent possible wrapping upon assignment to
s->length. */
+ ret = -EOVERFLOW;
+ goto out_restore_sg;
+ }
+
s->length = s_length;
/*
@@ -1493,7 +1500,18 @@ int iommu_dma_map_sg(struct device *dev, struct
scatterlist *sg, int nents,
* 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)) {
+ ret = -EOVERFLOW;
+ goto out_restore_sg;
+ }
+
+ prev->length = new_prev_len;
iova_len += pad_len;
}
--
2.34.1
