[PATCH] vfio/type1: validate dirty bitmap page size before use

[Yousef Alhouseen]

The dirty bitmap ioctl paths derive a shift with __ffs() from the
userspace supplied bitmap page size before comparing it with the IOMMU
page size. A zero page size has undefined behavior, and a non-power-of-2
value makes the bitmap size check use a different granularity than the
page size later accepted by the ioctl.

Reject invalid bitmap page sizes before using them in shift arithmetic.

Signed-off-by: Yousef Alhouseen <alhouseenyousef@xxxxxxxxx>
---
 drivers/vfio/vfio_iommu_type1.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index c8151ba54..9499381d0 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -26,6 +26,7 @@
 #include <linux/fs.h>
 #include <linux/highmem.h>
 #include <linux/iommu.h>
+#include <linux/log2.h>
 #include <linux/module.h>
 #include <linux/mm.h>
 #include <linux/kthread.h>
@@ -2949,6 +2950,9 @@ static int vfio_iommu_type1_unmap_dma(struct vfio_iommu *iommu,
 		if (!access_ok((void __user *)bitmap.data, bitmap.size))
 			return -EINVAL;
 
+		if (!is_power_of_2(bitmap.pgsize))
+			return -EINVAL;
+
 		pgshift = __ffs(bitmap.pgsize);
 		ret = verify_bitmap_size(unmap.size >> pgshift,
 					 bitmap.size);
@@ -3039,6 +3043,9 @@ static int vfio_iommu_type1_dirty_pages(struct vfio_iommu *iommu,
 			       range.bitmap.size))
 			return -EINVAL;
 
+		if (!is_power_of_2(range.bitmap.pgsize))
+			return -EINVAL;
+
 		pgshift = __ffs(range.bitmap.pgsize);
 		ret = verify_bitmap_size(size >> pgshift,
 					 range.bitmap.size);
-- 
2.54.0