[PATCH v1 0/2] userfaultfd: clear the inherited uffd bit in move_swap_pte()

[Donggeun Yoo]

UFFDIO_MOVE on a swapped-out page installs the source PTE at the
destination unchanged, so a uffd bit set on the source lands in a
destination VMA that was never registered for write protection, and
nothing clears it afterwards.  Patch 1 clears the bit unless the
destination is RWP-registered, which is what the present-page and
zeropage move paths already do.  Patch 2 adds the test that catches it.

x86_64 defconfig plus USERFAULTFD, TRANSPARENT_HUGEPAGE, GUP_TEST and a
swap device, under QEMU, base 17e7b8eacf4c:

  uffd-unit-tests                    before   after
  move-swap-wp on anon               not ok   ok
  the other 114 unit tests           ok       ok
  uffd-wp-mremap, 38 tests           ok       ok

  pagemap bit 57 at the destination  before   after
  swapped page, dst not armed        set      clear
  swapped page, dst WP-armed         set      clear
  swapped page, dst RWP-armed        set      set
  resident page, dst WP-armed        clear    clear

  MADV_COLLAPSE over 2 MB at dst     EINVAL   0

Donggeun Yoo (2):
  userfaultfd: clear the inherited uffd bit in move_swap_pte()
  selftests/mm: add a test for UFFDIO_MOVE of a write-protected swap
    entry

 mm/userfaultfd.c                             |  2 +
 tools/testing/selftests/mm/uffd-unit-tests.c | 61 ++++++++++++++++++++
 2 files changed, 63 insertions(+)


base-commit: 17e7b8eacf4cac800a4fc89a28729df72a2dabda
-- 
2.53.0