diff options
author | Eric Biggers <ebiggers@google.com> | 2023-09-25 08:54:51 +0300 |
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committer | Eric Biggers <ebiggers@google.com> | 2023-09-26 08:34:33 +0300 |
commit | 5b11888471806edf699316d4dcb9b426caebbef2 (patch) | |
tree | 1803e2ff78b2ea9cd71b8d562faa2f854165167c /fs/crypto/inline_crypt.c | |
parent | 7a0263dc904f3467f474e4088ae092eda9a5a99b (diff) | |
download | linux-5b11888471806edf699316d4dcb9b426caebbef2.tar.xz |
fscrypt: support crypto data unit size less than filesystem block size
Until now, fscrypt has always used the filesystem block size as the
granularity of file contents encryption. Two scenarios have come up
where a sub-block granularity of contents encryption would be useful:
1. Inline crypto hardware that only supports a crypto data unit size
that is less than the filesystem block size.
2. Support for direct I/O at a granularity less than the filesystem
block size, for example at the block device's logical block size in
order to match the traditional direct I/O alignment requirement.
(1) first came up with older eMMC inline crypto hardware that only
supports a crypto data unit size of 512 bytes. That specific case
ultimately went away because all systems with that hardware continued
using out of tree code and never actually upgraded to the upstream
inline crypto framework. But, now it's coming back in a new way: some
current UFS controllers only support a data unit size of 4096 bytes, and
there is a proposal to increase the filesystem block size to 16K.
(2) was discussed as a "nice to have" feature, though not essential,
when support for direct I/O on encrypted files was being upstreamed.
Still, the fact that this feature has come up several times does suggest
it would be wise to have available. Therefore, this patch implements it
by using one of the reserved bytes in fscrypt_policy_v2 to allow users
to select a sub-block data unit size. Supported data unit sizes are
powers of 2 between 512 and the filesystem block size, inclusively.
Support is implemented for both the FS-layer and inline crypto cases.
This patch focuses on the basic support for sub-block data units. Some
things are out of scope for this patch but may be addressed later:
- Supporting sub-block data units in combination with
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64, in most cases. Unfortunately this
combination usually causes data unit indices to exceed 32 bits, and
thus fscrypt_supported_policy() correctly disallows it. The users who
potentially need this combination are using f2fs. To support it, f2fs
would need to provide an option to slightly reduce its max file size.
- Supporting sub-block data units in combination with
FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32. This has the same problem
described above, but also it will need special code to make DUN
wraparound still happen on a FS block boundary.
- Supporting use case (2) mentioned above. The encrypted direct I/O
code will need to stop requiring and assuming FS block alignment.
This won't be hard, but it belongs in a separate patch.
- Supporting this feature on filesystems other than ext4 and f2fs.
(Filesystems declare support for it via their fscrypt_operations.)
On UBIFS, sub-block data units don't make sense because UBIFS encrypts
variable-length blocks as a result of compression. CephFS could
support it, but a bit more work would be needed to make the
fscrypt_*_block_inplace functions play nicely with sub-block data
units. I don't think there's a use case for this on CephFS anyway.
Link: https://lore.kernel.org/r/20230925055451.59499-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/crypto/inline_crypt.c')
-rw-r--r-- | fs/crypto/inline_crypt.c | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c index 7d9f6c167de5..8c6d37d6225a 100644 --- a/fs/crypto/inline_crypt.c +++ b/fs/crypto/inline_crypt.c @@ -43,6 +43,7 @@ static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci) { const struct super_block *sb = ci->ci_inode->i_sb; unsigned int flags = fscrypt_policy_flags(&ci->ci_policy); + int dun_bits; if (flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) return offsetofend(union fscrypt_iv, nonce); @@ -53,8 +54,9 @@ static unsigned int fscrypt_get_dun_bytes(const struct fscrypt_info *ci) if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) return sizeof(__le32); - /* Default case: IVs are just the file logical block number */ - return DIV_ROUND_UP(fscrypt_max_file_lblk_bits(sb), 8); + /* Default case: IVs are just the file data unit index */ + dun_bits = fscrypt_max_file_dun_bits(sb, ci->ci_data_unit_bits); + return DIV_ROUND_UP(dun_bits, 8); } /* @@ -126,7 +128,7 @@ int fscrypt_select_encryption_impl(struct fscrypt_info *ci) * crypto configuration that the file would use. */ crypto_cfg.crypto_mode = ci->ci_mode->blk_crypto_mode; - crypto_cfg.data_unit_size = sb->s_blocksize; + crypto_cfg.data_unit_size = 1U << ci->ci_data_unit_bits; crypto_cfg.dun_bytes = fscrypt_get_dun_bytes(ci); devs = fscrypt_get_devices(sb, &num_devs); @@ -165,7 +167,8 @@ int fscrypt_prepare_inline_crypt_key(struct fscrypt_prepared_key *prep_key, return -ENOMEM; err = blk_crypto_init_key(blk_key, raw_key, crypto_mode, - fscrypt_get_dun_bytes(ci), sb->s_blocksize); + fscrypt_get_dun_bytes(ci), + 1U << ci->ci_data_unit_bits); if (err) { fscrypt_err(inode, "error %d initializing blk-crypto key", err); goto fail; @@ -232,10 +235,11 @@ EXPORT_SYMBOL_GPL(__fscrypt_inode_uses_inline_crypto); static void fscrypt_generate_dun(const struct fscrypt_info *ci, u64 lblk_num, u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE]) { + u64 index = lblk_num << ci->ci_data_units_per_block_bits; union fscrypt_iv iv; int i; - fscrypt_generate_iv(&iv, lblk_num, ci); + fscrypt_generate_iv(&iv, index, ci); BUILD_BUG_ON(FSCRYPT_MAX_IV_SIZE > BLK_CRYPTO_MAX_IV_SIZE); memset(dun, 0, BLK_CRYPTO_MAX_IV_SIZE); |