iommu: Protect against overflow in iommu_pgsize()

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: b1d99dc5f983 ("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>

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 2bd668ae9466bb9aae96c214db37e7d5f946ade4..900fb782c3a6a175b5196cf40ff71ab447fa1278 100644 (file)
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2413,6 +2413,7 @@ static size_t iommu_pgsize(struct iommu_domain *domain, unsigned long iova,
        unsigned int pgsize_idx, pgsize_idx_next;
        unsigned long pgsizes;
        size_t offset, pgsize, pgsize_next;
+       size_t offset_end;
        unsigned long addr_merge = paddr | iova;
 
        /* Page sizes supported by the hardware and small enough for @size */
@@ -2453,7 +2454,8 @@ static size_t iommu_pgsize(struct iommu_domain *domain, unsigned long iova,
         * If size is big enough to accommodate the larger page, reduce
         * the number of smaller pages.
         */
-       if (offset + pgsize_next <= size)
+       if (!check_add_overflow(offset, pgsize_next, &offset_end) &&
+           offset_end <= size)
                size = offset;
 
 out_set_count: