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authorNadav Amit <namit@vmware.com>2022-04-21 16:35:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-04-21 20:01:09 -0700
commit0e88904cb700a9654c9f0d9ca4967e761e7c9ee8 (patch)
tree55b76001e346f77c3ffbee1ce480586d4060efad /mm
parent9b3016154c913b2e7ec5ae5c9a42eb9e732d86aa (diff)
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 <namit@vmware.com> Acked-by: Peter Xu <peterx@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/userfaultfd.c15
1 files changed, 9 insertions, 6 deletions
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);