Re: [RFC PATCH v2 2/2] dm-inlinecrypt: add target for inline block device encryption

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Oct 16, 2024 at 04:27:48PM -0700, Eric Biggers wrote:
> Add a new device-mapper target "dm-inlinecrypt" that is similar to
> dm-crypt but uses the blk-crypto API instead of the regular crypto API.
> This allows it to take advantage of inline encryption hardware such as
> that commonly built into UFS host controllers.

A slight difference in behavior vs. dm-crypt that I just became aware of:
dm-crypt allows XTS keys whose first half equals the second half, i.e.
cipher key == tweak key.  dm-inlinecrypt typically will not allow this.  Inline
encryption hardware typically rejects such keys, and blk-crypto-fallback rejects
them too because it uses CRYPTO_TFM_REQ_FORBID_WEAK_KEYS.

IMO, rejecting these weak keys is desirable, and the fact that dm-inlinecrypt
fixes this issue with dm-crypt will just need to be documented.

- Eric