Skip to content

Commit 6166c3c

Browse files
Gavin Guogregkh
Gavin Guo
authored andcommitted
mm/huge_memory: fix dereferencing invalid pmd migration entry
commit be6e843 upstream. When migrating a THP, concurrent access to the PMD migration entry during a deferred split scan can lead to an invalid address access, as illustrated below. To prevent this invalid access, it is necessary to check the PMD migration entry and return early. In this context, there is no need to use pmd_to_swp_entry and pfn_swap_entry_to_page to verify the equality of the target folio. Since the PMD migration entry is locked, it cannot be served as the target. Mailing list discussion and explanation from Hugh Dickins: "An anon_vma lookup points to a location which may contain the folio of interest, but might instead contain another folio: and weeding out those other folios is precisely what the "folio != pmd_folio((*pmd)" check (and the "risk of replacing the wrong folio" comment a few lines above it) is for." BUG: unable to handle page fault for address: ffffea60001db008 CPU: 0 UID: 0 PID: 2199114 Comm: tee Not tainted 6.14.0+ #4 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:split_huge_pmd_locked+0x3b5/0x2b60 Call Trace: <TASK> try_to_migrate_one+0x28c/0x3730 rmap_walk_anon+0x4f6/0x770 unmap_folio+0x196/0x1f0 split_huge_page_to_list_to_order+0x9f6/0x1560 deferred_split_scan+0xac5/0x12a0 shrinker_debugfs_scan_write+0x376/0x470 full_proxy_write+0x15c/0x220 vfs_write+0x2fc/0xcb0 ksys_write+0x146/0x250 do_syscall_64+0x6a/0x120 entry_SYSCALL_64_after_hwframe+0x76/0x7e The bug is found by syzkaller on an internal kernel, then confirmed on upstream. Link: https://lkml.kernel.org/r/[email protected] Link: https://lore.kernel.org/all/[email protected]/ Link: https://lore.kernel.org/all/[email protected]/ Fixes: 84c3fc4 ("mm: thp: check pmd migration entry in common path") Signed-off-by: Gavin Guo <[email protected]> Acked-by: David Hildenbrand <[email protected]> Acked-by: Hugh Dickins <[email protected]> Acked-by: Zi Yan <[email protected]> Reviewed-by: Gavin Shan <[email protected]> Cc: Florent Revest <[email protected]> Cc: Matthew Wilcox (Oracle) <[email protected]> Cc: Miaohe Lin <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
1 parent 2910019 commit 6166c3c

File tree

1 file changed

+8
-3
lines changed

1 file changed

+8
-3
lines changed

mm/huge_memory.c

Lines changed: 8 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2879,6 +2879,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
28792879
void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
28802880
pmd_t *pmd, bool freeze, struct folio *folio)
28812881
{
2882+
bool pmd_migration = is_pmd_migration_entry(*pmd);
2883+
28822884
VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio));
28832885
VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE));
28842886
VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
@@ -2889,9 +2891,12 @@ void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
28892891
* require a folio to check the PMD against. Otherwise, there
28902892
* is a risk of replacing the wrong folio.
28912893
*/
2892-
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
2893-
is_pmd_migration_entry(*pmd)) {
2894-
if (folio && folio != pmd_folio(*pmd))
2894+
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || pmd_migration) {
2895+
/*
2896+
* Do not apply pmd_folio() to a migration entry; and folio lock
2897+
* guarantees that it must be of the wrong folio anyway.
2898+
*/
2899+
if (folio && (pmd_migration || folio != pmd_folio(*pmd)))
28952900
return;
28962901
__split_huge_pmd_locked(vma, pmd, address, freeze);
28972902
}

0 commit comments

Comments
 (0)