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mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths 

commit f268f6cf87 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 f3f0e1d215
("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of
the security impact of this only came in commit 27e1f82731 ("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@google.com
Link: https://lkml.kernel.org/r/20221128180252.1684965-3-jannh@google.com
Link: https://lkml.kernel.org/r/20221125213714.4115729-3-jannh@google.com
Fixes: f3f0e1d215 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Jann Horn <jannh@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[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@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jann Horn 2022-11-25 22:37:14 +01:00 committed by Greg Kroah-Hartman
parent 588be4a04b
commit 275c626c13
1 changed files with 8 additions and 1 deletions
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9
mm/khugepaged.c
View File

@ -1302,13 +1302,20 @@ 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);
atomic_long_dec(&mm->nr_ptes);
tlb_remove_table_sync_one();
pte_free(mm, pmd_pgtable(_pmd));
mmu_notifier_invalidate_range_end(mm, addr,
end);
}
up_write(&mm->mmap_sem);
}