iommu/io-pgtable-dart: Fix off by one error in table index check

The check for the dart table index allowed values of
(1 << data->tbl_bits) while only as many entries are initialized in
apple_dart_alloc_pgtable. This results in an array out of bounds access
when data->tbl_bits is at its maximal value of 2. When data->tbl_bits is
0 or 1 an unset (initialized to zero) data->pgd[] entry is used. In both
cases the value is used as pointer to read page table entries and
results in dereferencing invalid pointers.
There is no prior check that the passed iova is inside the iommu's IAS
so invalid values can be passed from driver's calling iommu_map().

Fixes: 74a0e72 ("iommu/io-pgtable-dart: Add 4-level page table support")
Reported-by: Dan Carpenter <[email protected]>
Closes: https://lore.kernel.org/asahi/[email protected]/
Signed-off-by: Janne Grunau <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>

Author: jannau

drivers/iommu/io-pgtable-dart.c

@@ -177,7 +177,7 @@ static dart_iopte *dart_get_last(struct dart_io_pgtable *data, unsigned long iov
 	int level = data->levels;
 	int tbl = dart_get_index(data, iova, level);
 
-	if (tbl > (1 << data->tbl_bits))
+	if (tbl >= (1 << data->tbl_bits))
 		return NULL;
 
 	ptep = data->pgd[tbl];
@@ -246,7 +246,7 @@ static int dart_map_pages(struct io_pgtable_ops *ops, unsigned long iova,
 
 	tbl = dart_get_index(data, iova, level);
 
-	if (tbl > (1 << data->tbl_bits))
+	if (tbl >= (1 << data->tbl_bits))
 		return -ENOMEM;
 
 	ptep = data->pgd[tbl];