The eMMC inline crypto standard will only specify 32 DUN bits (a.k.a. IV
bits), unlike UFS's 64. IV_INO_LBLK_64 is therefore not applicable, but
an encryption format which uses one key per policy and permits the
moving of encrypted file contents (as f2fs's garbage collector requires)
is still desirable.
To support such hardware, add a new encryption format IV_INO_LBLK_32
that makes the best use of the 32 bits: the IV is set to
'SipHash-2-4(inode_number) + file_logical_block_number mod 2^32', where
the SipHash key is derived from the fscrypt master key. We hash only
the inode number and not also the block number, because we need to
maintain contiguity of DUNs to merge bios.
Unlike with IV_INO_LBLK_64, with this format IV reuse is possible; this
is unavoidable given the size of the DUN. This means this format should
only be used where the requirements of the first paragraph apply.
However, the hash spreads out the IVs in the whole usable range, and the
use of a keyed hash makes it difficult for an attacker to determine
which files use which IVs.
Besides the above differences, this flag works like IV_INO_LBLK_64 in
that on ext4 it is only allowed if the stable_inodes feature has been
enabled to prevent inode numbers and the filesystem UUID from changing.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20200515204141.251098-1-ebiggers@kernel.org
(Resolved conflicts with inline encryption support. Besides the
necessary "straightforward" merge resolutions, also made
fscrypt_get_dun_bytes() aware of IV_INO_LBLK_32 and made IV_INO_LBLK_32
usable with wrapped keys.)
Test: 'atest vts_kernel_encryption_test' on Cuttlefish with
the IV_INO_LBLK_32 test added (http://aosp/1315024).
Also tested enabling this in the fstab for Cuttlefish
(using http://aosp/1315886).
Also ran 'kvm-xfstests -c ext4,f2fs -g encrypt', including my
work-in-progress xfstest for IV_INO_LBLK_32.
Bug: 144046242
Change-Id: I57df71d502bde0475efc906a0812102063ff2f2a
Signed-off-by: Eric Biggers <ebiggers@google.com>
1583a39a85