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

[Milan Broz]

On 10/4/24 8:48 PM, Eric Biggers wrote:
> On Thu, Oct 03, 2024 at 10:44:07PM -0700, Christoph Hellwig wrote:
> > On Thu, Oct 03, 2024 at 05:41:52PM -0700, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@xxxxxxxxxx>
> > >
> > > 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.
> > >
> > > The table syntax matches dm-crypt's, but for now only a stripped-down
> > > set of parameters is supported.  For example, for now AES-256-XTS is the
> > > only supported cipher.
> >
> > Maybe I'm stepping into a mine-field here, but if this simply uses
> > blk-crypto to accellerate a subset of dm-crypt, why isn't dm-crypt
> > simply enhanced to use blk-crypto when available?
> > compatible,
>
> Milan Broz (cryptsetup maintainer) has said that he prefers a separate dm
> target.  See
> https://lore.kernel.org/dm-devel/9ef95bbc-4eee-4c00-f199-0daa3cdd03ed@xxxxxxxxx/
>
> That was a couple years ago though, and this discussion seems to have gone
> around in a circle.  Maybe things have changed.

There was another discussion recently. I also discussed this with Mikulas
as DM maintainer, and we agreed this is the best way.

Extending dm-crypt is possible, but the dm-crypt threat model should not allow
pushing plaintext down the level.
(I am currently investigating several issues with Opal hw encryption that just
cannot happen with sw dm-crypt. We opened can of worms supporting it in LUKS. :)

Actually, I like the inline encryption logic (and the sw fallback), just I would
prefer we clearly separate the code here (and dm-crypt is already complicated enough).

> A dm-crypt extension sounds fine to me too, though keep in mind there will
> eventually be inline crypto exclusive features such as hardware-wrapped keys.

Milan