iommufd: Don't overflow during division for dirty tracking

[ Upstream commit cb30dfa75d55eced379a42fd67bd5fb7ec38555e ]

If pgshift is 63 then BITS_PER_TYPE(*bitmap->bitmap) * pgsize will overflow
to 0 and this triggers divide by 0.

In this case the index should just be 0, so reorganize things to divide
by shift and avoid hitting any overflows.

Link: https://patch.msgid.link/r/0-v1-663679b57226+172-iommufd_dirty_div0_jgg@nvidia.com
Cc: stable@vger.kernel.org
Fixes: 58ccf0190d19 ("vfio: Add an IOVA bitmap support")
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reported-by: syzbot+093a8a8b859472e6c257@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=093a8a8b859472e6c257
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
[ drivers/iommu/iommufd/iova_bitmap.c => drivers/vfio/iova_bitmap.c ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/vfio/iova_bitmap.c b/drivers/vfio/iova_bitmap.c
index 76ef63b940d964d97e702abb95b7807c2eee577a..eab0de7799fa2757920d8e7e02354ef10d4d90cc 100644 (file)
--- a/drivers/vfio/iova_bitmap.c
+++ b/drivers/vfio/iova_bitmap.c
@@ -126,9 +126,8 @@ struct iova_bitmap {
 static unsigned long iova_bitmap_offset_to_index(struct iova_bitmap *bitmap,
                                                 unsigned long iova)
 {
-       unsigned long pgsize = 1UL << bitmap->mapped.pgshift;
-
-       return iova / (BITS_PER_TYPE(*bitmap->bitmap) * pgsize);
+       return (iova >> bitmap->mapped.pgshift) /
+              BITS_PER_TYPE(*bitmap->bitmap);
 }
 
 /*