[PATCH 6.6.y] mm: migrate_device: fix pte_pfn/pte_dirty called on non-present PTE

From: Kefeng Wang <[email protected]>

[ Upstream commit 63867c82d0c0c2d182016a32b1cc0103116b0ea5 ]

pte_pfn() and pte_dirty() have undefined behaviour when called on a
non-present PTE. In migrate_vma_collect_pmd(), these functions may be
invoked on non-present entries (e.g., device-private entries), leading
to potential crashes from pte_pfn() or incorrect dirty folio accounting
from pte_dirty(). Fix both by guarding with pte_present() checks.

Link: https://lore.kernel.org/[email protected]
Link: https://lore.kernel.org/[email protected]
Fixes: fd35ca3d12cc ("mm/migrate_device.c: copy pte dirty bit to page")
Fixes: 6c287605fd56 ("mm: remember exclusively mapped anonymous pages with PG_anon_exclusive")
Signed-off-by: Kefeng Wang <[email protected]>
Reviewed-by: Balbir Singh <[email protected]>
Acked-by: Zi Yan <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Matthew Brost <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Ying Huang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
[ adapted `folio_test_anon(folio)`/`folio_mark_dirty(folio)` context lines to 6.6's `PageAnon(page)`/`folio_mark_dirty(page_folio(page))` spelling since the `folio` local doesn't exist ]
Signed-off-by: Sasha Levin <[email protected]>
---
 mm/migrate_device.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index f209dc512d821..d4ee7ab735a38 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -194,7 +194,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			bool anon_exclusive;
 			pte_t swp_pte;
 
-			flush_cache_page(vma, addr, pte_pfn(pte));
+			if (pte_present(pte))
+				flush_cache_page(vma, addr, pte_pfn(pte));
 			anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
 			if (anon_exclusive) {
 				pte = ptep_clear_flush(vma, addr, ptep);
@@ -213,7 +214,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			migrate->cpages++;
 
 			/* Set the dirty flag on the folio now the pte is gone. */
-			if (pte_dirty(pte))
+			if (pte_present(pte) && pte_dirty(pte))
 				folio_mark_dirty(page_folio(page));
 
 			/* Setup special migration page table entry */
-- 
2.53.0