netdev - Re: [PATCH v4] mac80211: move extra crypto data off the stack

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Message-ID: <CAKv+Gu_jdiQn+o5PAZmPfMsQYt8PsOkDE6YNU11VH9WM_QPcvg@mail.gmail.com>
Date:   Mon, 17 Oct 2016 14:20:38 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     "<linux-wireless@...r.kernel.org>" <linux-wireless@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH v4] mac80211: move extra crypto data off the stack

On 17 October 2016 at 14:16, Johannes Berg <johannes@...solutions.net> wrote:
> On Mon, 2016-10-17 at 14:06 +0100, Ard Biesheuvel wrote:
>>
>> Actually, while I think it will be worthwhile going forward to
>> implement such an 'auxiliary data' feature in a generic way, I still
>> think we should address the issue at hand without too much
>> complication.
>>
>> If we pedal back to the version of 'mac80211: move struct aead_req
>> off the stack' that uses kzalloc() instead of aead_request_alloc(),
>> we can simply add some space for aad[] and/or zero[], and get rid of
>> the kmem cache entirely.
>>
>> If you're past this point already, i won't bother but otherwise I can
>> rework 'mac80211: move struct aead_req off the stack' so that the
>> other patch is no longer required (and IIRC, this is actually
>> something you proposed yourself a couple of iterations ago?)
>
> Yes, I did consider that.
>
> It makes some sense, and I guess the extra memcpy() would be cheaper
> than the extra alloc?
>
> I'd happily use that instead of the combination of my two patches. The
> aead_request_alloc() is just a simple inline anyway, so no real problem
> not using it.
>

Indeed. And it keeps the clutter inside the aes_xxx.c files, which
could easily be updated in the future to use some auxdata feature if
it ever materializes.

I think it would help this code, but also the ESP code you pointed
out, to have some kind of 'ordered synchronous' CRYPTO_xxx flag, where
the crypto API could manage the kmem cache and percpu pointers to
allocations. This goes well beyond what we can do as a fix, though, so
we need an intermediate solution in any case.

Shall I propose the patch?