tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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iommufd: Don't overflow during division for dirty tracking

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>

Jason Gunthorpe cb30dfa7 211ddde0

+2 -3
+2 -3
drivers/iommu/iommufd/iova_bitmap.c
··· 130 130 static unsigned long iova_bitmap_offset_to_index(struct iova_bitmap *bitmap, 131 131 unsigned long iova) 132 132 { 133 - unsigned long pgsize = 1UL << bitmap->mapped.pgshift; 134 - 135 - return iova / (BITS_PER_TYPE(*bitmap->bitmap) * pgsize); 133 + return (iova >> bitmap->mapped.pgshift) / 134 + BITS_PER_TYPE(*bitmap->bitmap); 136 135 } 137 136 138 137 /*