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authorAlex Williamson2022-08-29 21:05:40 -0600
committerAlex Williamson2022-08-31 08:57:30 -0600
commit873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4 (patch)
treeed1101504531fdfc35557bcf5c79a4b0bb165796 /drivers
parentb90cb1053190353cc30f0fef0ef1f378ccc063c5 (diff)
vfio/type1: Unpin zero pages
There's currently a reference count leak on the zero page. We increment the reference via pin_user_pages_remote(), but the page is later handled as an invalid/reserved page, therefore it's not accounted against the user and not unpinned by our put_pfn(). Introducing special zero page handling in put_pfn() would resolve the leak, but without accounting of the zero page, a single user could still create enough mappings to generate a reference count overflow. The zero page is always resident, so for our purposes there's no reason to keep it pinned. Therefore, add a loop to walk pages returned from pin_user_pages_remote() and unpin any zero pages. Cc: stable@vger.kernel.org Reported-by: Luboslav Pivarc <lpivarc@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/166182871735.3518559.8884121293045337358.stgit@omen Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/vfio/vfio_iommu_type1.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index db516c90a977..8706482665d1 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -558,6 +558,18 @@ static int vaddr_get_pfns(struct mm_struct *mm, unsigned long vaddr,
ret = pin_user_pages_remote(mm, vaddr, npages, flags | FOLL_LONGTERM,
pages, NULL, NULL);
if (ret > 0) {
+ int i;
+
+ /*
+ * The zero page is always resident, we don't need to pin it
+ * and it falls into our invalid/reserved test so we don't
+ * unpin in put_pfn(). Unpin all zero pages in the batch here.
+ */
+ for (i = 0 ; i < ret; i++) {
+ if (unlikely(is_zero_pfn(page_to_pfn(pages[i]))))
+ unpin_user_page(pages[i]);
+ }
+
*pfn = page_to_pfn(pages[0]);
goto done;
}