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
