linux-kernel - Re: [PATCH v4 11/14] treewide: Prepare to remove VLA usage for AHASH_REQUEST_ON

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Date:   Fri, 13 Jul 2018 11:44:06 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Kees Cook <keescook@...omium.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Alasdair Kergon <agk@...hat.com>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Lars Persson <larper@...s.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Rabin Vincent <rabinv@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>, qat-linux@...el.com,
        dm-devel@...hat.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 11/14] treewide: Prepare to remove VLA usage for
 AHASH_REQUEST_ON_STACK

On Thu, Jul 12, 2018 at 08:33:24PM -0700, Kees Cook wrote:
> On Thu, Jul 12, 2018 at 5:40 PM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> > On Thu, Jul 12, 2018 at 06:02:26PM +0200, Arnd Bergmann wrote:
> >>
> >> Looking through some of the drivers, I found this interesting one:
> >
> > As I said before these patches are fundamentally broken.  Users
> > of AHASH_REQUEST_ON_STACK can only use sync algorithm providers
> > and therefore drivers are irrelevant.
> 
> I don't understand what this means. Can you give an example of what
> you want to see happen that will accomplish the VLA removals?

Any algorithm that is async must be ignored when you're calculating
the maximum on-stack size of the request.  For example, sha512-mb
is marked as async and therefore must not be used in conjunction
with AHASH_REQUEST_ON_STACK.

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