Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   David Laight <David.Laight@ACULAB.COM>
To:     'Salvatore Mesoraca' <s.mesoraca16@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Kees Cook <keescook@chromium.org>,
        Eric Biggers <ebiggers3@gmail.com>,
        Laura Abbott <labbott@redhat.com>
Subject: RE: [PATCH v2 0/2] crypto: removing various VLAs
Thread-Topic: [PATCH v2 0/2] crypto: removing various VLAs
Thread-Index: AQHT0AqPFLFjzadDvEuYJrE7teT3QaP4fQXg
Date:   Mon, 9 Apr 2018 14:35:50 +0000
Message-ID: <ca31b95a8b8e4dab90c5ea2eb6e6477f@AcuMS.aculab.com>
References: <1523282087-22128-1-git-send-email-s.mesoraca16@gmail.com>
In-Reply-To: <1523282087-22128-1-git-send-email-s.mesoraca16@gmail.com>
Accept-Language: en-GB, en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
X-Authenticated_ID: 
X-PolicySMART: 3396946, 3397078
X-Virus-Status: Scanned by VirusSMART (s)
X-Virus-Status: Scanned by VirusSMART (c)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

From: Salvatore Mesoraca
> Sent: 09 April 2018 14:55
> 
> v2:
> 	As suggested by Herbert Xu, the blocksize and alignmask checks
> 	have been moved to crypto_check_alg.
> 	So, now, all the other separate checks are not necessary.
> 	Also, the defines have been moved to include/crypto/algapi.h.
> 
> v1:
> 	As suggested by Laura Abbott[1], I'm resending my patch with
> 	MAX_BLOCKSIZE and MAX_ALIGNMASK defined in an header, so they
> 	can be used in other places.
> 	I took this opportunity to deal with some other VLAs not
> 	handled in the old patch.

If the constants are visible they need better names.
Maybe CRYPTO_MAX_xxx.

You can also do much better than allocating MAX_BLOCKSIZE + MAX_ALIGNMASK
bytes by requesting 'long' aligned on-stack memory.
The easiest way is to define a union like:

union crypto_tmp {
	u8 buf[CRYPTO_MAX_TMP_BUF];
	long buf_align;
};

Then in each function:

	union tmp crypto_tmp;
	u8 *keystream = PTR_ALIGN(tmp.buf, alignmask + 1);

I think CRYPTO_MAX_TMP_BUF needs to be MAX_BLOCKSIZE + MAX_ALIGNMASK - sizeof (long).

	David