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/mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch
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@xxxxxxxxxx>
Subject: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths
Date: Wed, 23 Nov 2022 17:56:52 +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/20221123165652.2204925-5-jannh@xxxxxxxxxx
Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem p=
ages")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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
@@ -1421,6 +1421,7 @@ static void collapse_and_free_pmd(struct
{
pmd_t pmd;
struct mmu_gather tlb;
+ struct mmu_notifier_range range;
mmap_assert_write_locked(mm);
if (vma->vm_file)
@@ -1433,12 +1434,16 @@ static void collapse_and_free_pmd(struct
lockdep_assert_held_write(&vma->anon_vma->root->rwsem);
page_table_check_pte_clear_range(mm, addr, pmd);
+ mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, addr,
+ addr + HPAGE_PMD_SIZE);
+ mmu_notifier_invalidate_range_start(&range);
tlb_gather_mmu(&tlb, mm);
pmd = READ_ONCE(*pmdp);
pmd_clear(pmdp);
tlb_flush_pte_range(&tlb, addr, HPAGE_PMD_SIZE);
pte_free_tlb(&tlb, pmd_pgtable(pmd), addr);
tlb_finish_mmu(&tlb);
+ mmu_notifier_invalidate_range_end(&range);
mm_dec_nr_ptes(mm);
}
_
Patches currently in -mm which might be from jannh@xxxxxxxxxx are
mm-khugepaged-take-the-right-locks-for-page-table-retraction.patch
mmu_gather-use-macro-arguments-more-carefully.patch
mm-khugepaged-fix-gup-fast-interaction-by-freeing-ptes-via-mmu_gather.patch
mm-khugepaged-invoke-mmu-notifiers-in-shmem-file-collapse-paths.patch
