From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH 0/4] random,x86,kvm: Add and use MSR_KVM_GET_RNG_SEED Date: Wed, 16 Jul 2014 10:23:16 +0300 Message-ID: <20140716072315.GW18167@minantech.com> References: <20140716064110.GV18167@minantech.com> <53C62563.6050106@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andy Lutomirski , kvm@vger.kernel.org, "H. Peter Anvin" , Theodore Ts'o , linux-kernel@vger.kernel.org, Kees Cook , x86@kernel.org, Srivatsa Vaddagiri , Raghavendra K T To: Daniel Borkmann Return-path: Received: from mail-we0-f175.google.com ([74.125.82.175]:64728 "EHLO mail-we0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756546AbaGPHXX (ORCPT ); Wed, 16 Jul 2014 03:23:23 -0400 Received: by mail-we0-f175.google.com with SMTP id t60so448187wes.6 for ; Wed, 16 Jul 2014 00:23:22 -0700 (PDT) Content-Disposition: inline In-Reply-To: <53C62563.6050106@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Jul 16, 2014 at 09:10:27AM +0200, Daniel Borkmann wrote: > On 07/16/2014 08:41 AM, Gleb Natapov wrote: > >On Tue, Jul 15, 2014 at 07:48:06PM -0700, Andy Lutomirski wrote: > >>virtio-rng is both too complicated and insufficient for initial rng > >>seeding. It's far too complicated to use for KASLR or any other > >>early boot random number needs. It also provides /dev/random-style > >>bits, which means that making guest boot wait for virtio-rng is > >>unacceptably slow, and doing it asynchronously means that > >>/dev/urandom might be predictable when userspace starts. > >> > >>This introduces a very simple synchronous mechanism to get > >>/dev/urandom-style bits. > > > >Why can't you use RDRAND instruction for that? > > You mean using it directly? I think simply for the very same reasons > as in c2557a303a ... So you trust your hypervisor vendor more than you trust your CPU vendor? :) -- Gleb.