linux-kernel - Re: [PATCH v7] lib/crypto: blake2s: include as built-in

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Message-ID: <CAMj1kXFhygHnB12g9MD0wMo_deZ6xd7FMEzbrvEvKVtqYdskAQ@mail.gmail.com>
Date:   Tue, 4 Jan 2022 18:02:52 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH v7] lib/crypto: blake2s: include as built-in

On Tue, 4 Jan 2022 at 02:22, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Mon, Jan 03, 2022 at 01:31:52PM +0100, Jason A. Donenfeld wrote:
> > In preparation for using blake2s in the RNG, we change the way that it
> > is wired-in to the build system. Instead of using ifdefs to select the
> > right symbol, we use weak symbols. And because ARM doesn't need the
> > generic implementation, we make the generic one default only if an arch
> > library doesn't need it already, and then have arch libraries that do
> > need it opt-in. So that the arch libraries can remain tristate rather
> > than bool, we then split the shash part from the glue code.
> >
> > Acked-by: Ard Biesheuvel <ardb@...nel.org>
> > Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: Masahiro Yamada <masahiroy@...nel.org>
> > Cc: linux-kbuild@...r.kernel.org
> > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > Cc: linux-crypto@...r.kernel.org
> > Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> > ---
> > Herbert - As discussed, I still intend to take this via the
> > crng/random.git tree because it forms a dependency, and I'd like to send
> > a pull very early in the 5.17 cycle. I've taken some care to minimize
> > changes to the {arch/*/}crypto/Kconfig files, as you mentioned this
> > might cause some conflicts. Your tree should work cleanly on top of this
> > commit.
>
> Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
>
> > Changes v6->v7:
> > - Split arch shash implementations out from the glue code, so that they
> >   can remain as tristates, and we thus don't need to touch
> >   arch/*/crypto/Kconfig at all.
>
> This looks good to me although I confess that I haven't actually
> tried to build it :) Hopefully the build robots will take care of
> this.
>

The only downside here is that the ARM/x86 accelerated shashes and the
generic shash now use the same core transform, right? Given that the
generic blake2s shash is never used for anything in the kernel, the
only reason for its existence was to be able to use the randomized
crypto testing infrastructure to test the arch code.

Ergo, there is no point in retaining the blake2s shashes and we can
simply remove all of them. (Note that blake2b is used as an shash via
the crypto API by btrfs, but blake2s is only used via the library API)