fscrypt: add support for data_unit_size < fs_block_size

This patchset adds support for configuring the granularity of file contents encryption (a.k.a. the "crypto data unit size") to be less than the filesystem block size on ext4 and f2fs. The main use case for this is to support inline crypto hardware that only supports a data unit size that is less than the FS block size being used. Another possible use case is to support direct I/O on encrypted files without the FS block alignment restriction. Note that decreasing the crypto data unit size decreases efficiency, so this feature should only be used when needed.

For full details, see patch 5 which adds the actual feature. Patches 1-4 are preparatory patches.

I've written an xfstest that verifies that when a sub-block data unit size is selected, the data on-disk is encrypted correctly with that data unit size. I'll be sending that out separately. Other testing of this patchset with xfstests has gone well, though it turns out that some additional changes will be needed for a sub-block data unit size to work with the IV_INO_LBLK_* encryption settings. See patch 5 for details. This patchset focuses on basic sub-block data unit size support first.

This patchset will cause some conflicts in the extent-based encryption patches that the btrfs folks are working on, as both are touching file contents encryption, but logically they are orthogonal features.

This patchset is based on v6.6-rc3.

Changed in v3:
- Shortened 'legacy_key_prefix_for_backcompat' to 'legacy_key_prefix'
- Other miscellaneous cleanups
- Rebased onto v6.6-rc3

Changed in v2:
- Rebased onto v6.6-rc1 and took into account CephFS's recent addition of support for fscrypt
- Narrowed the focus somewhat by dropping the attempted support for IV_INO_LBLK_32 and clearly documenting what is considered out of scope for now
- Other cleanups

Eric Biggers (5):
fscrypt: make it clearer that key_prefix is deprecated
fscrypt: make the bounce page pool opt-in instead of opt-out
fscrypt: compute max_lblk_bits from s_maxbytes and block size
fscrypt: replace get_ino_and_lblk_bits with just has_32bit_inodes
fscrypt: support crypto data unit size less than filesystem block size

 Documentation/filesystems/fscrypt.rst | 117 ++++++++++++++------
 fs/ceph/crypto.c                      |   1 +
 fs/crypto/bio.c                       |  39 ++++---
 fs/crypto/crypto.c                    | 148 +++++++++++++++-----------
 fs/crypto/fscrypt_private.h           |  58 ++++++++--
 fs/crypto/inline_crypt.c              |  19 ++--
 fs/crypto/keysetup.c                  |   5 +
 fs/crypto/keysetup_v1.c               |   5 +-
 fs/crypto/policy.c                    |  73 +++++++++----
 fs/ext4/crypto.c                      |  13 +--
 fs/f2fs/super.c                       |  13 +--
 fs/ubifs/crypto.c                     |   3 +-
 include/linux/fscrypt.h               |  72 ++++++++-----
 include/uapi/linux/fscrypt.h          |   3 +-
 14 files changed, 364 insertions(+), 205 deletions(-)

base-commit: 6465e260f48790807eef06b583b38ca9789b6072

2.42.0



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