From patchwork Sun Oct 25 14:31:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arvind Sankar X-Patchwork-Id: 285401 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=-12.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, USER_AGENT_GIT 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 A587EC55178 for ; Sun, 25 Oct 2020 14:31:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BE472085B for ; Sun, 25 Oct 2020 14:31:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1415098AbgJYObj (ORCPT ); Sun, 25 Oct 2020 10:31:39 -0400 Received: from mail-qt1-f193.google.com ([209.85.160.193]:40116 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1414982AbgJYObj (ORCPT ); Sun, 25 Oct 2020 10:31:39 -0400 Received: by mail-qt1-f193.google.com with SMTP id m9so4899067qth.7; Sun, 25 Oct 2020 07:31:26 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=i4eX+361CNFGQN2UQLtgO0wdjlQPWSbW5hz94r5g1po=; b=tScp24scpYi2zAVXN+6cWi7UoQWz5yBBWFgZ5tgQ076hhFabZKGCc825tuzy2TNdz8 m3Lo/aDSMI6cWWTsIbNciemzSqHdZUcXRGBXZjqCFmNt+FlVQzqU/KeavkNjvQz+bepY ZyuC6lHp6yBc9mPbK6s/mE6jA/oRFWK/JsLL+Vb2IxL87srq0EV+t/kGYpIDL4svzKax eam5Z8LOGBVB9MF0CGT3ymIS/uj7CiCJ9gSczeoBjO85TTwXb7h06CIAADs9YTl1VW1a hwjFa2zrxgoAzNv9Dp+hQrn5IM5HW0VYaKhJxWoruxlmJj8x1TS5X3fEwl+1Y8TRkupS Amyg== X-Gm-Message-State: AOAM53350OucaiVPtJ1tYsA+NaaiePa8CgRCjE2OYSb8fCVZfWF1ggF5 u00/PyWcq8pA1L3ynFV3QTqLoJhfXuxTEQ== X-Google-Smtp-Source: ABdhPJzsyfCxly9OaP5gTUypi9SJ3XskYCAgFs2n8MAOXaQkSc0VJXtdrA9GC6ZXK/ovTZ5RkX0y+A== X-Received: by 2002:ac8:4e0d:: with SMTP id c13mr11383519qtw.382.1603636285799; Sun, 25 Oct 2020 07:31:25 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id s73sm4740898qke.71.2020.10.25.07.31.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Oct 2020 07:31:24 -0700 (PDT) From: Arvind Sankar To: Herbert Xu , "David S. Miller" , "linux-crypto@vger.kernel.org" , Eric Biggers , David Laight Cc: linux-kernel@vger.kernel.org, Eric Biggers Subject: [PATCH v4 3/6] crypto: lib/sha256 - Don't clear temporary variables Date: Sun, 25 Oct 2020 10:31:16 -0400 Message-Id: <20201025143119.1054168-4-nivedita@alum.mit.edu> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20201025143119.1054168-1-nivedita@alum.mit.edu> References: <20201025143119.1054168-1-nivedita@alum.mit.edu> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org 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 Reviewed-by: Eric Biggers Acked-by: Ard Biesheuvel --- 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)); }