[PATCH v2] vhost/vdpa: reject overflowing PA map page counts on 32-bit

[Yousef Alhouseen]

vhost_vdpa_pa_map() adds the IOVA page offset to the user-controlled map
size before computing the number of pages to pin. On 32-bit systems,
where unsigned long is narrower than u64, that addition can overflow and
the code can pin and map fewer pages than the requested IOTLB range.

Reject sizes that overflow the unsigned long page-count calculation.

Signed-off-by: Yousef Alhouseen <alhouseenyousef@xxxxxxxxx>
---
Changes in v2:
- Clarify that the overflow is on 32-bit systems.
- Drop the unrelated memlock check change.

 drivers/vhost/vdpa.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index ac55275fa..38b28ed3d 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1102,6 +1102,7 @@ static int vhost_vdpa_pa_map(struct vhost_vdpa *v,
 	unsigned int gup_flags = FOLL_LONGTERM;
 	unsigned long npages, cur_base, map_pfn, last_pfn = 0;
 	unsigned long lock_limit, sz2pin, nchunks, i;
+	unsigned long page_offset;
 	u64 start = iova;
 	long pinned;
 	int ret = 0;
@@ -1114,7 +1115,13 @@ static int vhost_vdpa_pa_map(struct vhost_vdpa *v,
 	if (perm & VHOST_ACCESS_WO)
 		gup_flags |= FOLL_WRITE;

-	npages = PFN_UP(size + (iova & ~PAGE_MASK));
+	page_offset = iova & ~PAGE_MASK;
+	if (size > ULONG_MAX - page_offset) {
+		ret = -EINVAL;
+		goto free;
+	}
+
+	npages = PFN_UP(size + page_offset);
 	if (!npages) {
 		ret = -EINVAL;
 		goto free;
-- 
2.54.0