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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 18AC5C5517A for ; Fri, 23 Oct 2020 22:11:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C8BA820724 for ; Fri, 23 Oct 2020 22:11:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603491091; bh=oYDdkAGeOEwqEQlJ3M1O6TGp5eWuctvbDWvQg3nFwJc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=CETqAMQmTe9hCbi+MR6NcFzu4RAgJMQR6Cys4vgfX1X0FeC+MkQBxX3Duy9SjhoFd 9vGX27c8W9wGRSRGkzFZl9sE4KgNmWZb63mTGX3AF+Q0yV2Mi/jFeVQ53+xHZCWy/A QrtOmpnEGnea5GxIgWHGVX6dG9uHgs7se8f3q/Z4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757063AbgJWWL3 (ORCPT ); Fri, 23 Oct 2020 18:11:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:56996 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757036AbgJWWL2 (ORCPT ); Fri, 23 Oct 2020 18:11:28 -0400 Received: from gmail.com (unknown [104.132.1.76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0AAA720724; Fri, 23 Oct 2020 22:11:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603491088; bh=oYDdkAGeOEwqEQlJ3M1O6TGp5eWuctvbDWvQg3nFwJc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=xxb/GAjvsPxTRs76hmFkdHimX18DvXWGGDbMDdK7f2OEgLtOzJAp9fOMx79mW5KDW jrF+kplGKkYgHIb12ePKpXbDRPxWF5qKWHe+jO3D2Sf+yoFJccO/pd/9RPWaYrAw18 eywmcxbINrfrNIQN0OFWYyur+NOhGakeNv7rhJsE= Date: Fri, 23 Oct 2020 15:11:26 -0700 From: Eric Biggers To: Arvind Sankar Cc: Herbert Xu , "David S. Miller" , "linux-crypto@vger.kernel.org" , David Laight , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/5] crypto: lib/sha256 - Don't clear temporary variables Message-ID: <20201023221126.GB180517@gmail.com> References: <20201023192203.400040-1-nivedita@alum.mit.edu> <20201023192203.400040-3-nivedita@alum.mit.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201023192203.400040-3-nivedita@alum.mit.edu> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 23, 2020 at 03:22:00PM -0400, Arvind Sankar wrote: > The assignments to clear a through h and t1/t2 are optimized out by the > compiler because they are unused after the assignments. > > Clearing individual scalar variables is unlikely to be useful, as they > may have been assigned to registers, and even if stack spilling was > required, there may be compiler-generated temporaries that are > impossible to clear in any case. > > So drop the clearing of a through h and t1/t2. > > Signed-off-by: Arvind Sankar > --- > lib/crypto/sha256.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/lib/crypto/sha256.c b/lib/crypto/sha256.c > index d43bc39ab05e..099cd11f83c1 100644 > --- a/lib/crypto/sha256.c > +++ b/lib/crypto/sha256.c > @@ -202,7 +202,6 @@ static void sha256_transform(u32 *state, const u8 *input) > state[4] += e; state[5] += f; state[6] += g; state[7] += h; > > /* clear any sensitive info... */ > - a = b = c = d = e = f = g = h = t1 = t2 = 0; > memzero_explicit(W, 64 * sizeof(u32)); > } Looks good, Reviewed-by: Eric Biggers