From: Hannes Frederic Sowa Subject: Re: [PATCH v2] crypto: memzero_explicit - make sure to clear out sensitive data Date: Mon, 08 Sep 2014 08:17:05 +0200 Message-ID: <1410157025.11627.10.camel@localhost> References: <1410125018-27277-1-git-send-email-dborkman@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: herbert@gondor.apana.org.au, tytso@mit.edu, linux-crypto@vger.kernel.org, gmazyland@gmail.com, Julia Lawall To: Daniel Borkmann Return-path: Received: from out4-smtp.messagingengine.com ([66.111.4.28]:35752 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751483AbaIHGWv (ORCPT ); Mon, 8 Sep 2014 02:22:51 -0400 Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by gateway2.nyi.internal (Postfix) with ESMTP id ED422206EC for ; Mon, 8 Sep 2014 02:17:07 -0400 (EDT) In-Reply-To: <1410125018-27277-1-git-send-email-dborkman@redhat.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On So, 2014-09-07 at 23:23 +0200, Daniel Borkmann wrote: > Recently, in commit 13aa93c70e71 ("random: add and use memzero_explicit() > for clearing data"), we have found that GCC may optimize some memset() > cases away when it detects a stack variable is not being used anymore > and going out of scope. This can happen, for example, in cases when we > are clearing out sensitive information such as keying material or any > e.g. intermediate results from crypto computations, etc. > > With the help of Coccinelle, we can figure out and fix such occurences > in the crypto subsytem as well. Julia Lawall provided the following > Coccinelle program: > > @@ > type T; > identifier x; > @@ > > T x; > ... when exists > when any > -memset > +memzero_explicit > (&x, > -0, > ...) > ... when != x > when strict > > @@ > type T; > identifier x; > @@ > > T x[...]; > ... when exists > when any > -memset > +memzero_explicit > (x, > -0, > ...) > ... when != x > when strict I think this Coccinelle patch won't make it completely unnecessary for a manual audit as it does not take optimizations (dead code eliminitation) into account? > > Therefore, make use of the drop-in replacement memzero_explicit() for > exactly such cases instead of using memset(). > > Signed-off-by: Daniel Borkmann > Cc: Julia Lawall > Cc: Herbert Xu > Cc: Theodore Ts'o > Cc: Hannes Frederic Sowa Acked-by: Hannes Frederic Sowa