The quilt patch titled
Subject: mm/hugetlb: fix uffd wr-protection for CoW optimization path
has been removed from the -mm tree. Its filename was
mm-hugetlb-fix-uffd-wr-protection-for-cow-optimization-path.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Peter Xu <peterx@xxxxxxxxxx>
Subject: mm/hugetlb: fix uffd wr-protection for CoW optimization path
Date: Tue, 21 Mar 2023 15:18:40 -0400
This patch fixes an issue that a hugetlb uffd-wr-protected mapping can be
writable even with uffd-wp bit set. It only happens with hugetlb private
mappings, when someone firstly wr-protects a missing pte (which will
install a pte marker), then a write to the same page without any prior
access to the page.
Userfaultfd-wp trap for hugetlb was implemented in hugetlb_fault() before
reaching hugetlb_wp() to avoid taking more locks that userfault won't
need. However there's one CoW optimization path that can trigger
hugetlb_wp() inside hugetlb_no_page(), which will bypass the trap.
This patch skips hugetlb_wp() for CoW and retries the fault if uffd-wp bit
is detected. The new path will only trigger in the CoW optimization path
because generic hugetlb_fault() (e.g. when a present pte was
wr-protected) will resolve the uffd-wp bit already. Also make sure
anonymous UNSHARE won't be affected and can still be resolved, IOW only
skip CoW not CoR.
This patch will be needed for v5.19+ hence copy stable.
[peterx@xxxxxxxxxx: v2]
Link: https://lkml.kernel.org/r/ZBzOqwF2wrHgBVZb@x1n
[peterx@xxxxxxxxxx: v3]
Link: https://lkml.kernel.org/r/20230324142620.2344140-1-peterx@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20230321191840.1897940-1-peterx@xxxxxxxxxx
Fixes: 166f3ecc0daf ("mm/hugetlb: hook page faults for uffd write protection")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reported-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Tested-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb-fix-uffd-wr-protection-for-cow-optimization-path
+++ a/mm/hugetlb.c
@@ -5478,7 +5478,7 @@ static vm_fault_t hugetlb_wp(struct mm_s
struct folio *pagecache_folio, spinlock_t *ptl)
{
const bool unshare = flags & FAULT_FLAG_UNSHARE;
- pte_t pte;
+ pte_t pte = huge_ptep_get(ptep);
struct hstate *h = hstate_vma(vma);
struct page *old_page;
struct folio *new_folio;
@@ -5488,6 +5488,17 @@ static vm_fault_t hugetlb_wp(struct mm_s
struct mmu_notifier_range range;
/*
+ * Never handle CoW for uffd-wp protected pages. It should be only
+ * handled when the uffd-wp protection is removed.
+ *
+ * Note that only the CoW optimization path (in hugetlb_no_page())
+ * can trigger this, because hugetlb_fault() will always resolve
+ * uffd-wp bit first.
+ */
+ if (!unshare && huge_pte_uffd_wp(pte))
+ return 0;
+
+ /*
* hugetlb does not support FOLL_FORCE-style write faults that keep the
* PTE mapped R/O such as maybe_mkwrite() would do.
*/
@@ -5500,7 +5511,6 @@ static vm_fault_t hugetlb_wp(struct mm_s
return 0;
}
- pte = huge_ptep_get(ptep);
old_page = pte_page(pte);
delayacct_wpcopy_start();
_
Patches currently in -mm which might be from peterx@xxxxxxxxxx are
mm-khugepaged-check-again-on-anon-uffd-wp-during-isolation.patch
mm-uffd-uffd_feature_wp_unpopulated.patch
mm-uffd-uffd_feature_wp_unpopulated-fix.patch
selftests-mm-smoke-test-uffd_feature_wp_unpopulated.patch
