From 0e88904cb700a9654c9f0d9ca4967e761e7c9ee8 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Thu, 21 Apr 2022 16:35:43 -0700 Subject: userfaultfd: mark uffd_wp regardless of VM_WRITE flag When a PTE is set by UFFD operations such as UFFDIO_COPY, the PTE is currently only marked as write-protected if the VMA has VM_WRITE flag set. This seems incorrect or at least would be unexpected by the users. Consider the following sequence of operations that are being performed on a certain page: mprotect(PROT_READ) UFFDIO_COPY(UFFDIO_COPY_MODE_WP) mprotect(PROT_READ|PROT_WRITE) At this point the user would expect to still get UFFD notification when the page is accessed for write, but the user would not get one, since the PTE was not marked as UFFD_WP during UFFDIO_COPY. Fix it by always marking PTEs as UFFD_WP regardless on the write-permission in the VMA flags. Link: https://lkml.kernel.org/r/20220217211602.2769-1-namit@vmware.com Fixes: 292924b26024 ("userfaultfd: wp: apply _PAGE_UFFD_WP bit") Signed-off-by: Nadav Amit Acked-by: Peter Xu Cc: Axel Rasmussen Cc: Mike Rapoport Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/userfaultfd.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) (limited to 'mm') diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 0cb8e5ef1713..e9bb6db002aa 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -72,12 +72,15 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd, _dst_pte = pte_mkdirty(_dst_pte); if (page_in_cache && !vm_shared) writable = false; - if (writable) { - if (wp_copy) - _dst_pte = pte_mkuffd_wp(_dst_pte); - else - _dst_pte = pte_mkwrite(_dst_pte); - } + + /* + * Always mark a PTE as write-protected when needed, regardless of + * VM_WRITE, which the user might change. + */ + if (wp_copy) + _dst_pte = pte_mkuffd_wp(_dst_pte); + else if (writable) + _dst_pte = pte_mkwrite(_dst_pte); dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); -- cgit v1.2.3