[PATCH 5.15.y 0/4] Backport series: "permit write-sealed memfd read-only shared mappings"

["Isaac J. Manjarres" <isaacmanjarres@google.com>]

Hello,

Until kernel version 6.7, a write-sealed memfd could not be mapped as
shared and read-only. This was clearly a bug, and was not inline with
the description of F_SEAL_WRITE in the man page for fcntl()[1].

Lorenzo's series [2] fixed that issue and was merged in kernel version
6.7, but was not backported to older kernels. So, this issue is still
present on kernels 5.4, 5.10, 5.15, 6.1, and 6.6.

This series consists of backports of two of Lorenzo's series [2] and
[3].

Note: for [2], I dropped the last patch in that series, since it
wouldn't make sense to apply it due to [4] being part of this tree. In
lieu of that, I backported [3] to ultimately allow write-sealed memfds
to be mapped as read-only.

[1] https://man7.org/linux/man-pages/man2/fcntl.2.html
[2] https://lore.kernel.org/all/913628168ce6cce77df7d13a63970bae06a526e0.1697116581.git.lstoakes@gmail.com/T/#m28fbfb0d5727e5693e54a7fb2e0c9ac30e95eca5
[3] https://lkml.kernel.org/r/99fc35d2c62bd2e05571cf60d9f8b843c56069e0.1732804776.git.lorenzo.stoakes@oracle.com
[4] https://lore.kernel.org/all/6e0becb36d2f5472053ac5d544c0edfe9b899e25.1730224667.git.lorenzo.stoakes@oracle.com/T/#u

Lorenzo Stoakes (4):
  mm: drop the assumption that VM_SHARED always implies writable
  mm: update memfd seal write check to include F_SEAL_WRITE
  mm: reinstate ability to map write-sealed memfd mappings read-only
  selftests/memfd: add test for mapping write-sealed memfd read-only

 fs/hugetlbfs/inode.c                       |  2 +-
 include/linux/fs.h                         |  4 +-
 include/linux/memfd.h                      | 14 ++++
 include/linux/mm.h                         | 80 +++++++++++++++-------
 kernel/fork.c                              |  2 +-
 mm/filemap.c                               |  2 +-
 mm/madvise.c                               |  2 +-
 mm/memfd.c                                 |  2 +-
 mm/mmap.c                                  | 10 ++-
 mm/shmem.c                                 |  2 +-
 tools/testing/selftests/memfd/memfd_test.c | 43 ++++++++++++
 11 files changed, 129 insertions(+), 34 deletions(-)

-- 
2.50.1.552.g942d659e1b-goog