linux-kernel - Re: [PATCH] crypto: ccm - avoid scatterlist for MAC encryption

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Message-ID: <CAKv+Gu9CppR+AN5_RdDJ6ZBRr1EDDLB+nABPddyaj5TKb5=j_Q@mail.gmail.com>
Date:   Wed, 19 Oct 2016 16:08:11 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Andy Lutomirski <luto@...capital.net>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        "<linux-wireless@...r.kernel.org>" <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jouni Malinen <j@...fi>
Subject: Re: [PATCH] crypto: ccm - avoid scatterlist for MAC encryption

On 19 October 2016 at 08:43, Johannes Berg <johannes@...solutions.net> wrote:
> On Wed, 2016-10-19 at 11:31 +0800, Herbert Xu wrote:
>> On Mon, Oct 17, 2016 at 06:21:14PM +0100, Ard Biesheuvel wrote:
>> >
>> >
>> > Annoyingly, all this complication with scatterlists etc is for
>> > doing
>> > asynchronous crypto via DMA capable crypto accelerators, and the
>> > networking code (ipsec as well as mac80211, afaik) only allow
>> > synchronous in the first place, given that they execute in softirq
>> > context.
>>
>> I'm still thinking about the issue (in particular, whether we
>> should continue to rely on the request context being SG-capable
>> or allow it to be on the stack for AEAD).
>
> :)
>
>> But IPsec definitely supports async crypto.  In fact it was the
>> very first user of async crypto.
>
> Yeah.
>

Ah yes, my bad.

>> mac80211 on the other hand is currently sync-only.
>
> We could probably make mac80211 do that too, but can we guarantee in-
> order processing? Anyway, it's pretty low priority, maybe never
> happening, since hardly anyone really uses "software" crypto, the wifi
> devices mostly have it built in anyway.
>

Indeed. The code is now correct in terms of API requirements, so let's
just wait for someone to complain about any performance regressions.