From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A3A96ECDFB8 for ; Wed, 18 Jul 2018 15:33:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 538AE20854 for ; Wed, 18 Jul 2018 15:33:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="Z3pyKlOg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 538AE20854 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731606AbeGRQMW (ORCPT ); Wed, 18 Jul 2018 12:12:22 -0400 Received: from mail-io0-f193.google.com ([209.85.223.193]:43244 "EHLO mail-io0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731588AbeGRQMW (ORCPT ); Wed, 18 Jul 2018 12:12:22 -0400 Received: by mail-io0-f193.google.com with SMTP id y10-v6so4440215ioa.10 for ; Wed, 18 Jul 2018 08:33:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=ItGYnOyuplg5zeX7jLigHkp90Z2TlK+7g801IPBHHMA=; b=Z3pyKlOgFBHdPdB55YUZdQICDgplLeYdraOa113wD9ezTNOH0ZAVPypj6mlNoMsGEH B8RnHaOfpqe5LEftSKNAlZhpXWXul5POwBJFjX4ICSXN5XsnYXDK6IzLjIQZpBJIHrro +Zu7y2JEy+bP2IFfSQI+gQa9B/YY+IrIRCuT8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=ItGYnOyuplg5zeX7jLigHkp90Z2TlK+7g801IPBHHMA=; b=OkaFdyzf79BmGpezcF1RxsXIhqYyKE2mNmTO26XLxcZ3BQGvKYFDKBkYictycG8+Rk rn6MaOP6WPzwPDTReK1IbD4Z1l6T5m8foazbljdLejinGQoJrUJ/yxyxXnszamt5lhAo YQctUBXX02Dc38FF28wrzdrMkQFuTDidGku4aZizF549dOMeiVjjLXvK46wYsI4aWc4S B312RuEXxHrdiCCOHyziuSAoizWxSVLDLIC9YbESuh1dnf3uiNBvpadSB697uAYec8nT 44GVv7d+UYu1aWMmYUpeQdZa2WmZZSLoG+Gr2ASfLaEobYeTc37+3Fcrl94yj/l3AcXk yaRg== X-Gm-Message-State: AOUpUlF2leISRAEMuYBiZdQxwihGC7SZIpZZaXu0mnQacpL7tqLFTmVL 7Ym57Pr5lkzevwr9NvLXQik1mRZ6y4L6gP/MYyLvFw== X-Google-Smtp-Source: AAOMgpdgZl8CdkkN4Tfuk23O6bgmU/s9zFlJHpHlafG0qrbZU4x7B/gANXiLb9YvGlqv3ucrWo+wla/qF7XXewu//hY= X-Received: by 2002:a6b:be83:: with SMTP id o125-v6mr5367001iof.173.1531928034941; Wed, 18 Jul 2018 08:33:54 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a6b:ac05:0:0:0:0:0 with HTTP; Wed, 18 Jul 2018 08:33:54 -0700 (PDT) In-Reply-To: References: <20180711203619.1020-1-keescook@chromium.org> <20180711203619.1020-12-keescook@chromium.org> <20180713004038.lwibdesz7ohhoind@gondor.apana.org.au> <20180713034406.zwu2pkp3f2onybxs@gondor.apana.org.au> <20180713052029.cfo24bsr5swtbdja@gondor.apana.org.au> From: Ard Biesheuvel Date: Thu, 19 Jul 2018 00:33:54 +0900 Message-ID: Subject: Re: [PATCH v4 11/14] treewide: Prepare to remove VLA usage for AHASH_REQUEST_ON_STACK To: Arnd Bergmann Cc: Kees Cook , Herbert Xu , "Gustavo A. R. Silva" , Eric Biggers , Alasdair Kergon , Giovanni Cabiddu , Lars Persson , Mike Snitzer , Rabin Vincent , Tim Chen , "David S. Miller" , Masahiro Yamada , "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" , qat-linux@intel.com, dm-devel@redhat.com, Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19 July 2018 at 00:33, Arnd Bergmann wrote: > On Wed, Jul 18, 2018 at 5:19 PM, Ard Biesheuvel > wrote: >> On 18 July 2018 at 23:50, Ard Biesheuvel wrote: >>> On 18 July 2018 at 05:59, Arnd Bergmann wrote: >>>> On Sun, Jul 15, 2018 at 6:28 AM, Kees Cook wrote: >>>>> >>>>> After my ahash to shash conversions, only ccm is left as an ahash >>>>> user, since it actually uses sg. But with the hard-coded value reduced >>>>> to 376, this doesn't trip the frame warnings any more. :) >>>>> >>>>> I'll send an updated series soon. >>>> >>>> Maybe we should get rid of that one as well then and remove >>>> AHASH_REQUEST_ON_STACK()? >>>> >>>> I see that Ard (now on Cc) added this usage only recently. Looking >>>> at the code some more, I also find that the descsize is probably >>>> much smaller than 376 for all possible cases of "cbcmac(*)", >>>> either alg->cra_blocksize plus a few bytes or sizeof(mac_desc_ctx) >>>> (i.e. 20) for arch/arm64/crypto/aes-glue.c. >>>> >>>> Walking the sglist here means open-coding a shash_ahash_update() >>>> implementation in crypto_ccm_auth(), that that doesn't seem to >>>> add much complexity over what it already has to do to chain >>>> the sglist today. >>>> >>> >>> It would be better to add a variably sized ahash request member to >>> struct crypto_ccm_req_priv_ctx, the only problem is that the last >>> member of that struct (skreq) is variably sized already, so it would >>> involve having a struct ahash_request pointer pointing into the same >>> struct, after the skreq member. >> >> Actually, I think the below should already do the trick: ahreq and >> skreq are not used at the same time, so we can stick them in a union, >> and take the max() of the reqsize to ensure there's enough empty space >> after it. > > This looks very nice indeed. > >> --------8<---------- >> diff --git a/crypto/ccm.c b/crypto/ccm.c >> index 0a083342ec8c..b242fd0d3262 100644 >> --- a/crypto/ccm.c >> +++ b/crypto/ccm.c >> @@ -50,7 +50,10 @@ struct crypto_ccm_req_priv_ctx { >> u32 flags; >> struct scatterlist src[3]; >> struct scatterlist dst[3]; >> - struct skcipher_request skreq; >> + union { >> + struct ahash_request ahreq; >> + struct skcipher_request skreq; >> + }; >> }; >> > > And this structure is never put on the stack anywhere but > always dynamically allocated anyway, right? > Yes.