The patch titled Subject: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Jann Horn jannh@google.com Subject: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths Date: Fri, 25 Nov 2022 22:37:14 +0100

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/20221125213714.4115729-3-jannh@google.com Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Jann Horn jannh@google.com Cc: David Hildenbrand david@redhat.com Cc: John Hubbard jhubbard@nvidia.com Cc: Peter Xu peterx@redhat.com Cc: Yang Shi <shy828301@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/khugepaged.c | 5 +++++ 1 file changed, 5 insertions(+)

--- a/mm/khugepaged.c~mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths +++ a/mm/khugepaged.c @@ -1399,6 +1399,7 @@ static void collapse_and_free_pmd(struct unsigned long addr, pmd_t *pmdp) { pmd_t pmd; + struct mmu_notifier_range range;

mmap_assert_write_locked(mm); if (vma->vm_file) @@ -1410,8 +1411,12 @@ static void collapse_and_free_pmd(struct if (vma->anon_vma) lockdep_assert_held_write(&vma->anon_vma->root->rwsem);

+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, addr, + addr + HPAGE_PMD_SIZE); + mmu_notifier_invalidate_range_start(&range); pmd = pmdp_collapse_flush(vma, addr, pmdp); tlb_remove_table_sync_one(); + mmu_notifier_invalidate_range_end(&range); mm_dec_nr_ptes(mm); page_table_check_pte_clear_range(mm, addr, pmd); pte_free(mm, pmd_pgtable(pmd)); _

Patches currently in -mm which might be from jannh@google.com are

mm-khugepaged-take-the-right-locks-for-page-table-retraction.patch mm-khugepaged-fix-gup-fast-interaction-by-sending-ipi.patch mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch