From 5ffc2a75534d9d74d49760f983f8eb675fa63d69 Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Tue, 6 Dec 2022 18:16:10 +0100 Subject: [PATCH] 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@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: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages") Signed-off-by: Jann Horn Acked-by: David Hildenbrand Reviewed-by: Yang Shi Cc: John Hubbard Cc: Peter Xu Cc: Signed-off-by: Andrew Morton [manual backport: this code was refactored from two copies into a common helper between 5.15 and 6.0] Signed-off-by: Jann Horn Signed-off-by: Sasha Levin --- mm/khugepaged.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index a8f2605cbd0d..8e67d2e5ff39 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -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 {