From: Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Antoine Tenart <antoine.tenart@bootlin.com>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
Pascal van Leeuwen <pascalvanl@gmail.com>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Eric Biggers <ebiggers@google.com>,
"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 2/3] crypto: inside-secure - Reduce stack usage
Date: Mon, 30 Sep 2019 21:09:10 +0000 [thread overview]
Message-ID: <CH2PR20MB29682E2C514733F290CFA3CECA820@CH2PR20MB2968.namprd20.prod.outlook.com> (raw)
In-Reply-To: <CAK8P3a0PeocENP6c=ENVrq2X8x-vinM6qhPRDDi_WEf6y73AOQ@mail.gmail.com>
> -----Original Message-----
> From: Arnd Bergmann <arnd@arndb.de>
> Sent: Monday, September 30, 2019 10:12 PM
> To: Pascal Van Leeuwen <pvanleeuwen@verimatrix.com>
> Cc: Antoine Tenart <antoine.tenart@bootlin.com>; Herbert Xu <herbert@gondor.apana.org.au>;
> David S. Miller <davem@davemloft.net>; Pascal van Leeuwen <pascalvanl@gmail.com>; Ard
> Biesheuvel <ard.biesheuvel@linaro.org>; Eric Biggers <ebiggers@google.com>; linux-
> crypto@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH 2/3] crypto: inside-secure - Reduce stack usage
>
> On Mon, Sep 30, 2019 at 9:04 PM Pascal Van Leeuwen
> <pvanleeuwen@verimatrix.com> wrote:
>
> > > Alternatively, it should be possible to shrink these allocations
> > > as the extra buffers appear to be largely unnecessary, but doing
> > > this would be a much more invasive change.
> > >
> > Actually, for HMAC-SHA512 you DO need all that buffer space.
> > You could shrink it to 2 * ctx->state_sz but then your simple indexing
> > is no longer going to fly. Not sure if that would be worth the effort.
>
> Stack allocations can no longer be dynamically sized in the kernel,
> so that would not work.
>
I was actually referring to your kzalloc, not to the original stack
based implementation ...
> What I noticed though is that the largest part of safexcel_ahash_export_state
> is used in the 'cache' member, and this is apparently only referenced inside of
> safexcel_hmac_init_iv, which you call twice. If that cache can be allocated
> only once, you save SHA512_BLOCK_SIZE bytes in one of the two paths.
>
Well ... hmmm ... "my"... This is not originally "my" code. And until you
brought this up, I did not fully realise it was using this export_state
struct to store those digests. Seems to have something to do with directly
taking the crypto_ahash_export state output, which is much more than that,
in case you need to continue the hash (which you don't here).
I guess you need to "catch" that output somewhere, so probably you could
save a bit of memory but I doubt it would be a significant improvement.
> > I don't like the part where you dynamically allocate the cryto_aes_ctx
> > though, I think that was not necessary considering its a lot smaller.
>
> I count 484 bytes for it, which is really large.
>
Maybe I should've counted myself ... totally unexpectedly huge. Why??
Anyway, glad I got rid of it already then.
> > And it conflicts with another change I have waiting that gets rid of
> > aes_expandkey and that struct alltogether (since it was really just
> > abused to do a key size check, which was very wasteful since the
> > function actually generates all roundkeys we don't need at all ...)
>
> Right, this is what I noticed there. With 480 of the 484 bytes gone,
> you are well below the warning limit even without the other change.
>
And by "other change" you mean the safexcel_ahash_export_state?
Ok, good to known, although I do like to improve that one as well,
but preferably by not exporting the cache so I don't need the full
struct.
Regards,
Pascal van Leeuwen
Silicon IP Architect, Multi-Protocol Engines @ Verimatrix
www.insidesecure.com
next prev parent reply other threads:[~2019-09-30 21:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-30 12:14 [PATCH 1/3] crypto: inside-secure - Fix a maybe-uninitialized warning Arnd Bergmann
2019-09-30 12:14 ` [PATCH 2/3] crypto: inside-secure - Reduce stack usage Arnd Bergmann
2019-09-30 19:04 ` Pascal Van Leeuwen
2019-09-30 20:11 ` Arnd Bergmann
2019-09-30 21:09 ` Pascal Van Leeuwen [this message]
2019-10-01 18:49 ` Arnd Bergmann
2019-10-10 12:40 ` Herbert Xu
2019-09-30 12:14 ` [PATCH 3/3] crypto: inside-secure - Remove #ifdef checks Arnd Bergmann
2019-09-30 13:04 ` Bjorn Helgaas
2019-10-10 12:55 ` Herbert Xu
2019-10-17 13:26 ` Pascal Van Leeuwen
2019-10-17 13:47 ` Arnd Bergmann
2019-10-17 14:14 ` Pascal Van Leeuwen
2019-09-30 18:50 ` [PATCH 1/3] crypto: inside-secure - Fix a maybe-uninitialized warning Pascal Van Leeuwen
2019-10-10 12:54 ` Herbert Xu
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