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Date:   Thu, 13 Sep 2018 16:18:28 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Andrew Lutomirski <luto@...nel.org>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Neves <sneves@....uc.pt>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>
Subject: Re: [PATCH net-next v3 02/17] zinc: introduce minimal cryptography library

On Thu, Sep 13, 2018 at 1:45 AM Andy Lutomirski <luto@...nel.org> wrote:
> I'm not convinced that there's any real need for *all* crypto
> algorithms to move into lib/zinc or to move at all.  As I see it,
> there are two classes of crypto algorithms in the kernel:
>
> a) Crypto that is used by code that chooses its algorithm statically
> and wants synchronous operations.  These include everything in
> drivers/char/random.c, but also a bunch of various networking things
> that are hardcoded and basically everything that uses stack buffers.
> (This means it includes all the code that I broke when I did
> VMAP_STACK.  Sign.)

Right, exactly. This is what will wind up using Zinc. I'm working on
an example usage of this for v4 of the patch submission, which you can
ogle in a preview here if you're curious:

https://git.zx2c4.com/linux-dev/commit/?h=big_key_rewrite

28 insertions, 206 deletions :-D

> b) Crypto that is used dynamically.  This includes dm-crypt
> (aes-xts-plain64, aes-cbc-essiv, etc), all the ALG_IF interfaces, a
> lot of IPSEC stuff, possibly KCM, and probably many more.  These will
> get comparatively little benefit from being converted to a zinc-like
> interface.  For some of these cases, it wouldn't make any sense at all
> to convert them.  Certainly the ones that do async hardware crypto
> using DMA engines will never look at all like zinc, even under the
> hood.

Right, this is what the crypto API will continue to be used for.


> I think that, as a short-term goal, it makes a lot of sense to have
> implementations of the crypto that *new* kernel code (like Wireguard)
> wants to use in style (a) that live in /lib, and it obviously makes
> sense to consolidate their implementations with the crypto/
> implementations in a timely manner.  As a medium-term goal, adding
> more algorithms as needed for things that could use the simpler APIs
> (Bluetooth, perhaps) would make sense.

Agreed 100%. With regards to "consolidate their implementations" --
I've actually already done this after your urging yesterday, and so
that will be a part of v4.

> But I see no reason at all that /lib should ever contain a grab-bag of
> crypto implementations just for the heck of it.  They should have real
> in-kernel users IMO.  And this means that there will probably always
> be some crypto implementations in crypto/ for things like aes-xts.

Right, precisely.

Jason

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