From: Herbert Xu Subject: Re: [PATCH v6 0/5] /dev/random - a new approach Date: Sun, 21 Aug 2016 11:14:39 +0800 Message-ID: <20160821031439.GA392@gondor.apana.org.au> References: <4723196.TTQvcXsLCG@positron.chronox.de> <20160811213632.GL10626@thunk.org> <20160817214254.GA22438@amd> <20160818172712.GA22054@thunk.org> <20160818183923.GA24817@amd> <20160819024947.GA10888@thunk.org> <20160819055612.GA20427@gondor.apana.org.au> <605855f7-2990-f118-c07c-ef20cfcc43fb@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Theodore Ts'o , Pavel Machek , Stephan Mueller , sandyinchina@gmail.com, Jason Cooper , John Denker , Joe Perches , George Spelvin , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org To: "H. Peter Anvin" Return-path: Received: from helcar.hengli.com.au ([209.40.204.226]:41349 "EHLO helcar.hengli.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752028AbcHUDPZ (ORCPT ); Sat, 20 Aug 2016 23:15:25 -0400 Content-Disposition: inline In-Reply-To: <605855f7-2990-f118-c07c-ef20cfcc43fb@linux.intel.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On Fri, Aug 19, 2016 at 10:20:18AM -0700, H. Peter Anvin wrote: > On 08/18/16 22:56, Herbert Xu wrote: > > On Thu, Aug 18, 2016 at 10:49:47PM -0400, Theodore Ts'o wrote: > >> > >> That really depends on the system. We can't assume that people are > >> using systems with a 100Hz clock interrupt. More often than not > >> people are using tickless kernels these days. That's actually the > >> problem with changing /dev/urandom to block until things are > >> initialized. > > > > Couldn't we disable tickless until urandom has been seeded? In fact > > perhaps we should accelerate the timer interrupt rate until it has > > been seeded? > > > > The biggest problem there is that the timer interrupt adds *no* entropy > unless there is a source of asynchronicity in the system. On PCs, > traditionally the timer has been run from a completely different crystal > (14.31818 MHz) than the CPU, which is the ideal situation, but if they > are run off the same crystal and run in lockstep, there is very little > if anything there. On some systems, the timer may even *be* the only > source of time, and the entropy truly is zero. Sure, but that's orthorgonal to what Ted was talking about above. Thanks, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt