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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Sat, 11 Mar 2023 09:55:15 +0100
Message-ID: <CAMj1kXG_27v0YXoO_8Avjcz=YtYhCfX_6pcXowk0fy5cYR6gVw@mail.gmail.com>
Subject: Re: [PATCH v2] crypto: lib - implement library version of AES in CFB mode
To:     Herbert Xu <herbert@gondor.apana.org.au>
Cc:     linux-crypto@vger.kernel.org, ebiggers@kernel.org,
        James Bottomley <James.Bottomley@hansenpartnership.com>
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On Sat, 11 Mar 2023 at 09:47, Herbert Xu <herbert@gondor.apana.org.au> wrote:
>
> On Sat, Mar 11, 2023 at 09:42:06AM +0100, Ard Biesheuvel wrote:
> >
> > Every call to crypto_skcipher_set_reqsize(), no?
>
> We'd only convert the software implementations.  But you're right
> there does seem to be a few users such as aria that demand a large
> amount of temp space.  I'd be tempted to just leave them on skcipher.
>
> In other cases such as ctr we can easily put the IV on the stack.
>

But why can't we make skcipher just a hybrid?

- make the scatterlist members in skcipher_request unions with virtual
src and dst alternatives
- add an API that assigns those alternative members and checks that
the tfm is not ALG_ASYNC
- make the existing skcipher_en/decrypt() implementations check the
request type, and hand off to a 'sync' alternative that allocates the
request ctx on the stack, and make the accessor return the stack
version instead of the heap version
- update skcipher_walk_xxx() to return the virtually addressable dst
and src if the sync request type is encountered.

That way, the skcipher implementations can remain as they are, and the
callers can just put a struct skcipher_request on the stack (without
the padding and ctx overhead) and call the new interface with virtual
addresses.

That way, all the SYNC_SKCIPHER hacks can go, and we don't need yet
another algo type.


That way, the implementations can remain the same,