iommu: Protect against overflow in iommu_pgsize()

[ Upstream commit e586e229 ]

On a 32 bit system calling:
 iommu_map(0, 0x40000000)

When using the AMD V1 page table type with a domain->pgsize of 0xfffff000
causes iommu_pgsize() to miscalculate a result of:
  size=0x40000000 count=2

count should be 1. This completely corrupts the mapping process.

This is because the final test to adjust the pagesize malfunctions when
the addition overflows. Use check_add_overflow() to prevent this.

Fixes: b1d99dc5 ("iommu: Hook up '->unmap_pages' driver callback")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/0-v1-3ad28fc2e3a3+163327-iommu_overflow_pgsize_jgg@nvidia.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>