Patch "mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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-col.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.



commit ce8cd48d81d003fb25e67bdcf6b20b1144fa7e6b
Author: Jann Horn <jannh@xxxxxxxxxx>
Date:   Tue Dec 6 18:16:08 2022 +0100

    mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths
    
    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: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 561660966435..b1fed0d2439b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1290,13 +1290,20 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 		 */
 		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);
 		}