Scatter gather lists can be created with more available entries than are
actually used (e.g. using sg_init_table() to reserve a specific number
of sg entries, but in actuality using something less than that based on
the data length). The caller sometimes fails to mark the last entry
with sg_mark_end(). In these cases, sg_nents() will return the original
size of the sg list as opposed to the actual number of sg entries that
contain valid data.
On arm64, if the sg_nents() value is used in a call to dma_map_sg() in
this situation, then it causes a BUG_ON in lib/swiotlb.c because an
"empty" sg list entry results in dma_capable() returning false and
swiotlb trying to create a bounce buffer of size 0. This occurred in
the userspace crypto interface before being fixed by
0f477b655a52 ("crypto: algif - Mark sgl end at the end of data")
Protect against this by using the new sg_nents_for_len() function which
returns only the number of sg entries required to meet the desired
length and supplying that value to dma_map_sg().
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
drivers/crypto/ccp/ccp-ops.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
index 542453c..d09c6c4 100644
--- a/drivers/crypto/ccp/ccp-ops.c
+++ b/drivers/crypto/ccp/ccp-ops.c
@@ -52,7 +52,7 @@ struct ccp_dm_workarea {
struct ccp_sg_workarea {
struct scatterlist *sg;
- unsigned int nents;
+ int nents;
struct scatterlist *dma_sg;
struct device *dma_dev;
@@ -495,7 +495,10 @@ static int ccp_init_sg_workarea(struct ccp_sg_workarea *wa, struct device *dev,
if (!sg)
return 0;
- wa->nents = sg_nents(sg);
+ wa->nents = sg_nents_for_len(sg, len);
+ if (wa->nents < 0)
+ return wa->nents;
+
wa->bytes_left = len;
wa->sg_used = 0;
--
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