[0/5] 4.19 backports of fixes for "CoW after fork() issue"

Message

Suren Baghdasaryan April 1, 2021, 6:21 p.m. UTC

We received a report that the copy-on-write issue repored by Jann Horn in
https://bugs.chromium.org/p/project-zero/issues/detail?id=2045 is still
reproducible on 4.14 and 4.19 kernels (the first issue with the reproducer
coded in vmsplice.c). I confirmed this and also that the issue was not
reproducible with 5.10 kernel. I tracked the fix to the following patch
introduced in 5.9 which changes the do_wp_page() logic:

09854ba94c6a 'mm: do_wp_page() simplification'

I backported this patch (#2 in the series) along with 2 prerequisite patches
(#1 and #4) that keep the backports clean and two followup fixes to the main
patch (#3 and #5). I had to skip the following fix:

feb889fb40fa 'mm: don't put pinned pages into the swap cache'

because it uses page_maybe_dma_pinned() which does not exists in earlier
kernels. Because pin_user_pages() does not exist there as well, I *think*
we can safely skip this fix on older kernels, but I would appreciate if
someone could confirm that claim.

The patchset cleanly applies over: stable linux-4.19.y, tag: v4.19.184

Note: 4.14 and 4.19 backports are very similar, so while I backported
only to these two versions I think backports for other versions can be
done easily.

Kirill Tkhai (1):
  mm: reuse only-pte-mapped KSM page in do_wp_page()

Linus Torvalds (2):
  mm: do_wp_page() simplification
  mm: fix misplaced unlock_page in do_wp_page()

Nadav Amit (1):
  mm/userfaultfd: fix memory corruption due to writeprotect

Shaohua Li (1):
  userfaultfd: wp: add helper for writeprotect check

 include/linux/ksm.h           |  7 ++++
 include/linux/userfaultfd_k.h | 10 ++++++
 mm/ksm.c                      | 30 ++++++++++++++++--
 mm/memory.c                   | 60 ++++++++++++++++-------------------
 4 files changed, 73 insertions(+), 34 deletions(-)