From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:58160) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TT7lB-0001Mg-MS for qemu-devel@nongnu.org; Tue, 30 Oct 2012 05:05:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TT7l5-0001EH-Kt for qemu-devel@nongnu.org; Tue, 30 Oct 2012 05:05:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8495) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TT7l5-0001Dl-CB for qemu-devel@nongnu.org; Tue, 30 Oct 2012 05:05:15 -0400 Message-ID: <508F9847.6030702@redhat.com> Date: Tue, 30 Oct 2012 10:05:11 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <604401631.2277495.1351264128301.JavaMail.root@redhat.com> <871ugl44v5.fsf@codemonkey.ws> <508AB5C0.2000304@zytor.com> <508ADD66.5040909@redhat.com> <5ea4bbfb-b761-42ef-93f8-7c91fee0bb30@email.android.com> <508AE9A6.4060304@redhat.com> <508AF2C0.30404@zytor.com> <508E4215.6050803@redhat.com> <508F5B07.8070008@zytor.com> In-Reply-To: <508F5B07.8070008@zytor.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 0/6] add paravirtualization hwrng support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "H. Peter Anvin" Cc: Amit Shah , Anthony Liguori , Andreas Faerber , qemu-devel@nongnu.org Il 30/10/2012 05:43, H. Peter Anvin ha scritto: > Let me be more specific. > > First of all, feeding /dev/urandom to the guest is dangerous -- you are > feeding it PRNG contents but telling it that it is real entropy. This > is a security hole. > > Second of all, you're doing something pointless: you are still > exhausting the entropy pool on the host at the same rate, and all you > end up with is something that isn't what you want. You still have the > same DoS on the host /dev/random that you're worried about. > > Third, you're doing something inefficient: you're running a PRNG in the > host which could be run more efficiently in guest space. Either you're not reading what I wrote, or you're confusing me with someone else. I *never* mentioned passing /dev/urandom, and in fact I explained to Anthony that it is wrong. Please take a look at http://permalink.gmane.org/gmane.comp.emulators.qemu/178123 What I said that passing /dev/hwrng or rdrand would: - not make /dev/random with virtio-rng-pci worse than without - make migration working - avoiding denial of service for the host's /dev/random > From an Intel perspective I guess I should be happy, as it functionally > would mean that unless you have RDRAND in the host you're insecure, but > I'd much rather see the Right Thing done. :) Paolo