From: Alex Williamson <alex.williamson@xxxxxxxxxx>
Subject: intel-iommu: fix off-by-one in pagetable freeing
dma_pte_free_level() has an off-by-one error when checking whether a pte
is completely covered by a range. Take for example the case of attempting
to free pfn 0x0 - 0x1ff, ie. 512 entries covering the first 2M superpage.
The level_size() is 0x200 and we test:
static void dma_pte_free_level(...
...
if (!(0 > 0 || 0x1ff < 0 + 0x200)) {
...
}
Clearly the 2nd test is true, which means we fail to take the branch to
clear and free the pagetable entry. As a result, we're leaking pagetables
and failing to install new pages over the range.
This was found with a PCI device assigned to a QEMU guest using vfio-pci
without a VGA device present. The first 1M of guest address space is
mapped with various combinations of 4K pages, but eventually the range is
entirely freed and replaced with a 2M contiguous mapping. intel-iommu
errors out with something like:
ERROR: DMA PTE for vPFN 0x0 already set (to 5c2b8003 not 849c00083)
In this case 5c2b8003 is the pointer to the previous leaf page that was
neither freed nor cleared and 849c00083 is the superpage entry that we're
trying to replace it with.
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Joerg Roedel <joro@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/iommu/intel-iommu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN drivers/iommu/intel-iommu.c~intel-iommu-fix-off-by-one-in-pagetable-freeing drivers/iommu/intel-iommu.c
--- a/drivers/iommu/intel-iommu.c~intel-iommu-fix-off-by-one-in-pagetable-freeing
+++ a/drivers/iommu/intel-iommu.c
@@ -917,7 +917,7 @@ static void dma_pte_free_level(struct dm
/* If range covers entire pagetable, free it */
if (!(start_pfn > level_pfn ||
- last_pfn < level_pfn + level_size(level))) {
+ last_pfn < level_pfn + level_size(level) - 1)) {
dma_clear_pte(pte);
domain_flush_cache(domain, pte, sizeof(*pte));
free_pgtable_page(level_pte);
_
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html