From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34069) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ar2DA-0005NP-Bg for qemu-devel@nongnu.org; Fri, 15 Apr 2016 07:46:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ar2D6-0004n0-A5 for qemu-devel@nongnu.org; Fri, 15 Apr 2016 07:46:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38107) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ar2D6-0004mw-4I for qemu-devel@nongnu.org; Fri, 15 Apr 2016 07:46:52 -0400 Date: Fri, 15 Apr 2016 12:46:46 +0100 From: "Richard W.M. Jones" Message-ID: <20160415114646.GY11600@redhat.com> References: <5710C55E.3030000@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5710C55E.3030000@redhat.com> Subject: Re: [Qemu-devel] RFC: virtio-rng and /dev/urandom List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cole Robinson , sgrubb@redhat.com Cc: libvirt-list@redhat.com, qemu-devel , "Daniel P. Berrange" , Peter Krempa , Amit Shah , mik@miknet.net, jjaburek@redhat.com, hkario@redhat.com, hpa@zytor.com, Paolo Bonzini , Eric Blake On Fri, Apr 15, 2016 at 06:41:34AM -0400, Cole Robinson wrote: > Libvirt currently rejects using host /dev/urandom as an input source for a > virtio-rng device. The only accepted sources are /dev/random and /dev/hwrng. > This is the result of discussions on qemu-devel around when the feature was > first added (2013). Examples: > > http://lists.gnu.org/archive/html/qemu-devel/2012-09/msg02387.html > https://lists.gnu.org/archive/html/qemu-devel/2013-03/threads.html#00023 > > libvirt's rejection of /dev/urandom has generated some complaints from users: > > https://bugzilla.redhat.com/show_bug.cgi?id=1074464 > * cited: http://www.2uo.de/myths-about-urandom/ > http://www.redhat.com/archives/libvir-list/2016-March/msg01062.html > http://www.redhat.com/archives/libvir-list/2016-April/msg00186.html > > I think it's worth having another discussion about this, at least with a > recent argument in one place so we can put it to bed. I'm CCing a bunch of > people. I think the questions are: > > 1) is the original recommendation to never use virtio-rng+/dev/urandom correct? > > 2) regardless of #1, should we continue to reject that config in libvirt? There was a lot of internal-to-Red Hat discussion on this which I can't reproduce here unfortunately. However the crux of it was that it's quite safe to read enormous amounts from /dev/urandom, even without adding any entropy at all, and use those numbers for cryptographic purposes. Steve: can we disclose the research that was done into this? If so can you summarise the results for us? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v