[PATCH v2 0/2] ext4: support encryption with blocksize != PAGE_SIZE

[Eric Biggers <ebiggers@kernel.org>]

Hello,

This patchset makes ext4 support encryption on filesystems where the
filesystem block size is not equal to PAGE_SIZE.  This allows e.g.
PowerPC systems to use ext4 encryption.

Most of the work for this was already done in prior kernel releases; now
the only part missing is decryption support in block_read_full_page().
Chandan Rajendra has proposed a patchset "Consolidate FS read I/O
callbacks code" [1] to address this and do various other things like
make ext4 use mpage_readpages() again, and make ext4 and f2fs share more
code.  But it doesn't seem to be going anywhere.

Therefore, I propose we simply add decryption support to
block_read_full_page() for now.  This is a fairly small change, and it
gets ext4 encryption with subpage-sized blocks working.

Note: to keep things simple I'm just allocating the work object from the
bi_end_io function with GFP_ATOMIC.  But if people think it's necessary,
it could be changed to use preallocation like the page-based read path.

Tested with 'gce-xfstests -c ext4/encrypt_1k -g auto', using the new
"encrypt_1k" config I created.  All tests pass except for those that
already fail or are excluded with the encrypt or 1k configs, and 2 tests
that try to create 1023-byte symlinks which fails since encrypted
symlinks are limited to blocksize-3 bytes.  Also ran the dedicated
encryption tests using 'kvm-xfstests -c ext4/1k -g encrypt'; all pass,
including the on-disk ciphertext verification tests.

[1] https://lkml.kernel.org/linux-fsdevel/20190910155115.28550-1-chandan@linux.ibm.com/T/#u

Changed v1 => v2:
  - Added check for S_ISREG() which technically should be there, though
    it happens not to matter currently.

Chandan Rajendra (1):
  ext4: Enable encryption for subpage-sized blocks

Eric Biggers (1):
  fs/buffer.c: support fscrypt in block_read_full_page()

 Documentation/filesystems/fscrypt.rst |  4 +--
 fs/buffer.c                           | 48 ++++++++++++++++++++++++---
 fs/ext4/super.c                       |  7 ----
 3 files changed, 45 insertions(+), 14 deletions(-)

-- 
2.23.0