From: Stephan Mueller Subject: Re: [BUG/PATCH] kernel RNG and its secrets Date: Fri, 10 Apr 2015 16:09:10 +0200 Message-ID: <1697288.aUGCRhyl06@tauon> References: <20150318095345.GA12923@zoho.com> <2792913.x6Cv5ZCyOY@tauon> <1428674403.3377.4.camel@stressinduktion.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: Daniel Borkmann , mancha , tytso@mit.edu, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au, dborkman@redhat.com To: Hannes Frederic Sowa Return-path: Received: from mail.eperm.de ([89.247.134.16]:34086 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932699AbbDJOJN (ORCPT ); Fri, 10 Apr 2015 10:09:13 -0400 In-Reply-To: <1428674403.3377.4.camel@stressinduktion.org> Sender: linux-crypto-owner@vger.kernel.org List-ID: Am Freitag, 10. April 2015, 16:00:03 schrieb Hannes Frederic Sowa: Hi Hannes, >On Fr, 2015-04-10 at 15:25 +0200, Stephan Mueller wrote: >> I would like to bring up that topic again as I did some more analyses: >> >> For testing I used the following code: >> >> static inline void memset_secure(void *s, int c, size_t n) >> { >> >> memset(s, c, n); >> >> BARRIER >> >> } >> >> where BARRIER is defined as: >> >> (1) __asm__ __volatile__("" : "=r" (s) : "0" (s)); >> >> (2) __asm__ __volatile__("": : :"memory"); >> >> (3) __asm__ __volatile__("" : "=r" (s) : "0" (s) : "memory"); > >Hm, I wonder a little bit... > >Could you quickly test if you replace (s) with (n) just for the fun of >it? I don't know if we should ask clang people about that, at least it >is their goal to be as highly compatible with gcc inline asm. Using __asm__ __volatile__("" : "=r" (n) : "0" (n) : "memory"); clang O2/3: no mov gcc O2/3: mov present ==> not good Using __asm__ __volatile__("" : "=r" (n) : "0" (n)); clang O2/3: no mov gcc O2/3: no mov ==> not good What do you expect that change shall do? > >Thanks for looking into this! > >Bye, >Hannes Ciao Stephan