linux-kernel - Re: [PATCH v2 2/4] crypto: skcipher - Enforce non-ASYNC for on-stack requests

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Message-ID: <20180911055334.py26ff7rib3sla2c@gondor.apana.org.au>
Date:   Tue, 11 Sep 2018 13:53:34 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Kees Cook <keescook@...omium.org>
Cc:     Eric Biggers <ebiggers@...gle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Gilad Ben-Yossef <gilad@...yossef.com>,
        Alexander Stein <alexander.stein@...tec-electronic.com>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Arnaud Ebalard <arno@...isbad.org>,
        Corentin Labbe <clabbe.montjoie@...il.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Christian Lamparter <chunkeey@...il.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/4] crypto: skcipher - Enforce non-ASYNC for on-stack
 requests

On Fri, Sep 07, 2018 at 09:02:45AM -0700, Kees Cook wrote:
>
> I'll continue to investigate alternatives, but I wanted to point out
> that the struct change actually fills an existing padding byte (so no
> change in memory usage) and marking this as an unlikely() test means
> it wouldn't even be measurable due to the branch predictor (so no
> change in speed). encrypt/decrypt entry is a tiny tiny fraction of the
> actual work done during encryption/decryption, etc.

The point is the ON_STACK request stuff is purely for backwards
compatibility and we don't want it to proliferate and pollute the
core API.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt