linux-kernel - Re: [RFC PATCH v2 0/4] Exporting existing crypto API code through zinc

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Message-ID: <CAKv+Gu-SHS2tF665dfqSgmH5EF5vGVtef=3_4WgCE=+8+Jw7Rw@mail.gmail.com>
Date:   Tue, 20 Nov 2018 11:32:05 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Eric Biggers <ebiggers@...nel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>, linux-fscrypt@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Crowley <paulcrowley@...gle.com>,
        Greg Kaiser <gkaiser@...gle.com>,
        Samuel Neves <samuel.c.p.neves@...il.com>,
        Tomer Ashur <tomer.ashur@...t.kuleuven.be>,
        Martin Willi <martin@...ongswan.org>
Subject: Re: [RFC PATCH v2 0/4] Exporting existing crypto API code through zinc

On Tue, 20 Nov 2018 at 07:02, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Mon, Nov 19, 2018 at 01:24:51PM +0800, Herbert Xu wrote:
> >
> > In response to Martin's patch-set which I merged last week, I think
> > here is quick way out for the zinc interface.
> >
> > Going through the past zinc discussions it would appear that
> > everybody is quite happy with the zinc interface per se.  The
> > most contentious areas are in fact the algorithm implementations
> > under zinc, as well as the conversion of the crypto API algorithms
> > over to using the zinc interface (e.g., you can no longer access
> > specific implementations).
> >
> > My proposal is to merge the zinc interface as is, but to invert
> > how we place the algorithm implementations.  IOW the implementations
> > should stay where they are now, with in the crypto API.  However,
> > we will provide direct access to them for zinc without going through
> > the crypto API.  IOW we'll just export the functions directly.
> >
> > Here is a proof of concept patch to do it for chacha20-generic.
> > It basically replaces patch 3 in the October zinc patch series.
> > Actually this patch also exports the arm/x86 chacha20 functions
> > too so they are ready for use by zinc.
> >
> > If everyone is happy with this then we can immediately add the
> > zinc interface and expose the existing crypto API algorithms
> > through it.  This would allow wireguard to be merged right away.
> >
> > In parallel, the discussions over replacing the implementations
> > underneath can carry on without stalling the whole project.
> >
> > PS This patch is totally untested :)
>
> Here is an updated version demonstrating how we could access the
> accelerated versions of chacha20.  It also includes a final patch
> to deposit the new zinc version of x86-64 chacha20 into
> arch/x86/crypto where it can be used by both the crypto API as well
> as zinc.
>
> The key differences between this and the last zinc patch series:
>
> 1. The crypto API algorithms remain individually accessible, this
> is crucial as these algorithm names are exported to user-space so
> changing the names to foo-zinc is not going to work.
>

Are you saying user space may use names like "ctr-aes-neon" directly
rather than "ctr(aes)" for any implementation of the mode?

If so, that is highly unfortunate, since it means we'd be breaking
user space by wrapping a crypto library function with its own arch
specific specializations into a generic crypto API wrapper.

Note that I think that using AF_ALG to access software crypto routines
(as opposed to accelerators) is rather pointless to begin with, but if
it permits that today than we're stuck with it.

> 2. The arch-specific algorithm code lives in their own module rather
> than in a monolithic module.
>

This is one of the remaining issues I have with Zinc. However, modulo
the above concerns, I think it does make sense to have a separate
function API for synchronous software routines below the current
crypto API. What I don't want is a separate Zinc kingdom with a
different name, different maintainers and going through a different
tree, and with its own approach to test vectors, arch specific code,
etc etc