From: Nadav Amit namit@vmware.com
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.
Fixes: 292924b26024 ("userfaultfd: wp: apply _PAGE_UFFD_WP bit") Cc: Mike Rapoport rppt@linux.vnet.ibm.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: Peter Xu peterx@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Nadav Amit namit@vmware.com --- mm/userfaultfd.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 0780c2a57ff1..885e5adb0168 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);