From aaf7f535d42dc2407ee38aa53d9383d3d1a0c220 Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Tue, 21 Mar 2023 15:18:40 -0400 Subject: [PATCH] mm/hugetlb: fix uffd wr-protection for CoW optimization path This patch fixes an issue that a hugetlb uffd-wr-protected mapping can be writable even with uffd-wp bit set. It only happens with hugetlb private mappings, when someone firstly wr-protects a missing pte (which will install a pte marker), then a write to the same page without any prior access to the page. Userfaultfd-wp trap for hugetlb was implemented in hugetlb_fault() before reaching hugetlb_wp() to avoid taking more locks that userfault won't need. However there's one CoW optimization path that can trigger hugetlb_wp() inside hugetlb_no_page(), which will bypass the trap. This patch skips hugetlb_wp() for CoW and retries the fault if uffd-wp bit is detected. The new path will only trigger in the CoW optimization path because generic hugetlb_fault() (e.g. when a present pte was wr-protected) will resolve the uffd-wp bit already. Also make sure anonymous UNSHARE won't be affected and can still be resolved, IOW only skip CoW not CoR. This patch will be needed for v5.19+ hence copy stable. Link: https://lkml.kernel.org/r/20230321191840.1897940-1-peterx@redhat.com Fixes: 166f3ecc0daf ("mm/hugetlb: hook page faults for uffd write protection") Signed-off-by: Peter Xu Reported-by: Muhammad Usama Anjum Tested-by: Muhammad Usama Anjum Acked-by: David Hildenbrand Reviewed-by: Mike Kravetz Cc: Andrea Arcangeli Cc: Axel Rasmussen Cc: Mike Rapoport Cc: Nadav Amit Cc: Signed-off-by: Andrew Morton --- mm/hugetlb.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 07abcb6eb203..61ee4930e686 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5478,7 +5478,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, struct folio *pagecache_folio, spinlock_t *ptl) { const bool unshare = flags & FAULT_FLAG_UNSHARE; - pte_t pte; + pte_t pte, newpte; struct hstate *h = hstate_vma(vma); struct page *old_page; struct folio *new_folio; @@ -5622,8 +5622,10 @@ retry_avoidcopy: mmu_notifier_invalidate_range(mm, range.start, range.end); page_remove_rmap(old_page, vma, true); hugepage_add_new_anon_rmap(new_folio, vma, haddr); - set_huge_pte_at(mm, haddr, ptep, - make_huge_pte(vma, &new_folio->page, !unshare)); + newpte = make_huge_pte(vma, &new_folio->page, !unshare); + if (huge_pte_uffd_wp(pte)) + newpte = huge_pte_mkuffd_wp(newpte); + set_huge_pte_at(mm, haddr, ptep, newpte); folio_set_hugetlb_migratable(new_folio); /* Make the old page be freed below */ new_folio = page_folio(old_page); -- 2.50.1