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

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Date:   Thu, 13 Sep 2018 09:46:17 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Eric Biggers <ebiggers@...gle.com>,
        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>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <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 Mon, Sep 10, 2018 at 10:52 PM, Herbert Xu
<herbert@...dor.apana.org.au> wrote:
> On Fri, Sep 07, 2018 at 08:56:23AM +0200, Ard Biesheuvel wrote:
>>
>> OK, so given that all SKCIPHER_REQUEST_ON_STACK occurrences are
>> updated in this series anyway, perhaps we should add
>> skcipher_[en|de]crypt_onstack() flavors that encapsulate the
>> additional check? Only question is how to enforce at compile time that
>> those are used instead of the ordinary ones when using a stack
>> allocated request. Would you mind using some macro foo here involving
>> __builtin_types_compatible_p() ?
>
> Something like a completely new type which in reality is just a
> wrapper around skcipher:
>
>         struct crypto_sync_skcipher {
>                 struct crypto_skcipher base;
>         } tfm;
>
>         tfm = crypto_alloc_sync_skcipher(...);
>
>         crypto_sync_skcipher_encrypt(...)
>         crypto_sync_skcipher_decrypt(...)
>
> These functions would just be trivial inline functions around their
> crypto_skcipher counterparts.

This means new wrappers for the other helpers too, yes? For example:

        SKCIPHER_REQUEST_ON_STACK(nreq, ctx->null);

        skcipher_request_set_tfm(nreq, ctx->null);
        skcipher_request_set_callback(nreq, req->base.flags, NULL, NULL);
        skcipher_request_set_crypt(nreq, req->src, req->dst, nbytes, NULL);

        return crypto_skcipher_encrypt(nreq);

For the above, we'd also need:

sync_skcipher_request_set_tfm()
sync_skcipher_request_set_callback()
sync_skcipher_request_set_crypt()

-Kees

-- 
Kees Cook
Pixel Security