From: Stephan Mueller Subject: Re: [BUG/PATCH] kernel RNG and its secrets Date: Fri, 10 Apr 2015 16:36:31 +0200 Message-ID: <2115964.QxtQ6rHSkc@tauon> References: <20150318095345.GA12923@zoho.com> <1697288.aUGCRhyl06@tauon> <1428675960.3377.8.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: In-Reply-To: <1428675960.3377.8.camel@stressinduktion.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org Am Freitag, 10. April 2015, 16:26:00 schrieb Hannes Frederic Sowa: Hi Hannes, >On Fr, 2015-04-10 at 16:09 +0200, Stephan Mueller wrote: >> 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 > >I suspected a problem in how volatile with non-present output args could >be different, but this seems not to be the case. > >I would contact llvm/clang mailing list and ask. Maybe there is a >problem? It seems kind of strange to me... Do you really think this is a compiler issue? I would rather think it is how to interpret the pure "memory" asm option. Thus, I would rather think that both, gcc and clang are right and we just need to use the code that fits both. > >Thanks, >Hannes > > >-- >To unsubscribe from this list: send the line "unsubscribe linux-crypto" in >the body of a message to majordomo@vger.kernel.org >More majordomo info at http://vger.kernel.org/majordomo-info.html Ciao Stephan