Re: [PATCH 2/3] AF_ALG: Drop support for off-CPU cryptography

[Eric Biggers <ebiggers@kernel.org>]

On Sat, Jul 25, 2026 at 03:04:43PM -0700, Eric Biggers wrote:
> If needed, "cbc(paes)" and/or "cbc-paes-caam" (whichever name it is
> being accessed as) can be allowed as a special case, as a stop-gap.
> 
> This would need confirmed use of that specific algorithm with upstream,
> which we don't quite have yet.  Dominique had a confirmed use of
> "tk(cbc(aes))", but that has never existed upstream in the first place,
> so it's not something that could be allowlisted upstream.
> 
> You've only mentioned that it "can" be used in this way in upstream.
> Can you confirm that it *is* used, and with an actual upstream algorithm
> name, and if so which one(s)?  And if so, would you also be able to
> share whether this is for dm-crypt or not?  We should remember that
> dm-crypt accepts keys directly and AF_ALG is not needed to use it.

We'd also need to know whether the user (if there is one) requires
unprivileged use.

Hopefully not: these sorts of hardware crypto drivers have lots of bugs.
Indeed, the CAAM "cbc(paes)" doesn't validate the key length correctly,
leaks DMA mappings, concurrent requests race with each other, etc...

- Eric