path: root/mm
diff options
authorMel Gorman <>2014-10-02 19:47:41 +0100
committerLinus Torvalds <>2014-10-02 11:57:18 -0700
commitd3cb8bf6081b8b7a2dabb1264fe968fd870fa595 (patch)
tree50783c31445c93012fe0ded14d4a49a03e0d504c /mm
parent50dddff3cb9af328dd42bafe3437c7f47e8b38a9 (diff)
mm: migrate: Close race between migration completion and mprotect
A migration entry is marked as write if pte_write was true at the time the entry was created. The VMA protections are not double checked when migration entries are being removed as mprotect marks write-migration-entries as read. It means that potentially we take a spurious fault to mark PTEs write again but it's straight-forward. However, there is a race between write migrations being marked read and migrations finishing. This potentially allows a PTE to be write that should have been read. Close this race by double checking the VMA permissions using maybe_mkwrite when migration completes. [ use maybe_mkwrite] Cc: Signed-off-by: Mel Gorman <> Acked-by: Rik van Riel <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm')
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/migrate.c b/mm/migrate.c
index f78ec9bd454d..2740360cd216 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -146,8 +146,11 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
if (pte_swp_soft_dirty(*ptep))
pte = pte_mksoft_dirty(pte);
+ /* Recheck VMA as permissions can change since migration started */
if (is_write_migration_entry(entry))
- pte = pte_mkwrite(pte);
+ pte = maybe_mkwrite(pte, vma);
if (PageHuge(new)) {
pte = pte_mkhuge(pte);