linux-kernel - Re: [PATCH] crypto: gcm

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Message-ID: <CAKv+Gu-3zzN=cikd4PftCVo2fJi9t_0kqZHBQncjokYQV5wVnA@mail.gmail.com>
Date:   Thu, 30 May 2019 16:11:37 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Iuliana Prodan <iuliana.prodan@....com>,
        Eric Biggers <ebiggers@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Horia Geanta <horia.geanta@....com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH] crypto: gcm - fix cacheline sharing

On Thu, 30 May 2019 at 15:58, Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Thu, May 30, 2019 at 01:45:47PM +0000, Iuliana Prodan wrote:
> >
> > On the current structure of caamalg, to work, iv needs to be copied
> > before memcpy(iv, req->iv, ivsize), from skcipher_edesc_alloc function.
> > For this we need edesc, but this cannot be allocated before knowing how
> > much memory we need. So, to make it work, we'll need to modify more in CAAM.
>
> All the copying does is:
>
>         if (ivsize)
>                 scatterwalk_map_and_copy(req->iv, req->src, req->cryptlen -
>                                          ivsize, ivsize, 0);
>
> Why do you need to allocate the edesc before doing this?
>

Because that is where the incoming iv is currently consumed. Copying
it out like this wipes the input IV from memory.