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

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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 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]
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Jann Horn 2022-12-06 18:16:10 +01:00 committed by Greg Kroah-Hartman
parent 48b00ceb54
commit 5ffc2a7553
1 changed files with 13 additions and 0 deletions
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13
mm/khugepaged.c
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@ -1313,6 +1313,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
spinlock_t *ptl;
int count = 0;
int i;
struct mmu_notifier_range range;
if (!vma || !vma->vm_file ||
vma->vm_start > haddr || vma->vm_end < haddr + HPAGE_PMD_SIZE)
@ -1406,9 +1407,13 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
}
/* step 4: collapse pmd */
mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, haddr,
haddr + HPAGE_PMD_SIZE);
mmu_notifier_invalidate_range_start(&range);
_pmd = pmdp_collapse_flush(vma, haddr, pmd);
mm_dec_nr_ptes(mm);
tlb_remove_table_sync_one();
mmu_notifier_invalidate_range_end(&range);
pte_free(mm, pmd_pgtable(_pmd));
i_mmap_unlock_write(vma->vm_file->f_mapping);
@ -1493,11 +1498,19 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
*/
if (down_write_trylock(&mm->mmap_sem)) {
if (!khugepaged_test_exit(mm)) {
struct mmu_notifier_range range;
mmu_notifier_range_init(&range,
MMU_NOTIFY_CLEAR, 0,
NULL, mm, addr,
addr + HPAGE_PMD_SIZE);
mmu_notifier_invalidate_range_start(&range);
/* assume page table is clear */
_pmd = pmdp_collapse_flush(vma, addr, pmd);
mm_dec_nr_ptes(mm);
tlb_remove_table_sync_one();
pte_free(mm, pmd_pgtable(_pmd));
mmu_notifier_invalidate_range_end(&range);
}
up_write(&mm->mmap_sem);
} else {