This is a note to let you know that I've just added the patch titled
mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From f268f6cf875f3220afc77bdd0bf1bb136eb54db9 Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@xxxxxxxxxx>
Date: Fri, 25 Nov 2022 22:37:14 +0100
Subject: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths
From: Jann Horn <jannh@xxxxxxxxxx>
commit f268f6cf875f3220afc77bdd0bf1bb136eb54db9 upstream.
Any codepath that zaps page table entries must invoke MMU notifiers to
ensure that secondary MMUs (like KVM) don't keep accessing pages which
aren't mapped anymore. Secondary MMUs don't hold their own references to
pages that are mirrored over, so failing to notify them can lead to page
use-after-free.
I'm marking this as addressing an issue introduced in commit f3f0e1d2150b
("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of
the security impact of this only came in commit 27e1f8273113 ("khugepaged:
enable collapse pmd for pte-mapped THP"), which actually omitted flushes
for the removal of present PTEs, not just for the removal of empty page
tables.
Link: https://lkml.kernel.org/r/20221129154730.2274278-3-jannh@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221128180252.1684965-3-jannh@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221125213714.4115729-3-jannh@xxxxxxxxxx
Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
[manual backport: this code was refactored from two copies into a common
helper between 5.15 and 6.0;
pmd collapse for PTE-mapped THP was only added in 5.4;
MMU notifier API changed between 4.19 and 5.4]
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1303,13 +1303,20 @@ static void retract_page_tables(struct a
*/
if (down_write_trylock(&mm->mmap_sem)) {
if (!khugepaged_test_exit(mm)) {
- spinlock_t *ptl = pmd_lock(mm, pmd);
+ spinlock_t *ptl;
+ unsigned long end = addr + HPAGE_PMD_SIZE;
+
+ mmu_notifier_invalidate_range_start(mm, addr,
+ end);
+ ptl = pmd_lock(mm, pmd);
/* assume page table is clear */
_pmd = pmdp_collapse_flush(vma, addr, pmd);
spin_unlock(ptl);
mm_dec_nr_ptes(mm);
tlb_remove_table_sync_one();
pte_free(mm, pmd_pgtable(_pmd));
+ mmu_notifier_invalidate_range_end(mm, addr,
+ end);
}
up_write(&mm->mmap_sem);
}
Patches currently in stable-queue which might be from jannh@xxxxxxxxxx are
queue-4.19/mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch
queue-4.19/mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch
