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

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Message-ID: <20241017194415.GA11717@sol.localdomain>
Date: Thu, 17 Oct 2024 12:44:15 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: dm-devel@...ts.linux.dev
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	Md Sadre Alam <quic_mdalam@...cinc.com>,
	Israel Rukshin <israelr@...dia.com>,
	Milan Broz <gmazyland@...il.com>,
	Mikulas Patocka <mpatocka@...hat.com>
Subject: Re: [RFC PATCH v2 2/2] dm-inlinecrypt: add target for inline block
 device encryption

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