From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42837) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fXTMn-0002bJ-3N for qemu-devel@nongnu.org; Mon, 25 Jun 2018 11:25:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fXTMj-0007Rn-UK for qemu-devel@nongnu.org; Mon, 25 Jun 2018 11:25:21 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:58196 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fXTMj-0007Re-Ol for qemu-devel@nongnu.org; Mon, 25 Jun 2018 11:25:17 -0400 Date: Mon, 25 Jun 2018 16:25:13 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180625152513.GI18580@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] Choosing PCR banks for swtpm's TPM 2 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Berger Cc: tpm2@lists.01.org, Kenneth Goldman , Chris Friesen , "Qi, Yadong" , qemu-devel , "Xu, Quan" , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau On Mon, Jun 25, 2018 at 11:05:55AM -0400, Stefan Berger wrote: > Hi! >=20 > =C2=A0I am sending this email to solicit input on the choice of the PCR= banks to > enable for swtpm's TPM 2. I have currently enabled 4 PCR banks for > SHA{1,256,384,512}. The downside of this is that running the TPM 2 with= so > many PCR banks has a performance impact when the Linux integrity measur= ement > architecture is used and has to extend measurements into all PCR banks, > which Linux does already. >=20 > TPM 2 has the PCR_Allocate() command for a user to select the PCR banks= to > use. This command allows to make some PCR banks invisible. The change h= as to > be done through the firmware and has the downside that the TPM2 does no= t > support TPM2_Shutdown(SU_STATE) after this command was used. This preve= nts > suspend/resume from working properly. So, it seems that one shouldn't h= ave > to use this command, which in turn means the number of PCR banks should= be > small. >=20 > Another complication with the swtpm is the upgrade path. Suspended VMs = will > expect that the PCR banks that were available before the suspend will b= e > available after the resume and a possible swtpm upgrade. This in turn m= eans > that the PCR banks should be chosen now and we'll have to stick with th= em. Anything that has a risk of needing to change between versions would need to be tied into the machine type in some way. >=20 > That said, my suggestion would be to enable only PCR banks for SHA256 f= or > 'now' and SHA512 for the future. Having two PCR banks should enable dec= ent > performance. If someone wants to have better performance he will have t= o go > through the firmware to select the PCR banks at the expense of loosing > suspend/resume support. >=20 > The change of PCR banks for the current 4 PCR banks will break the stat= e of > all swtpms. >=20 > If you have suggestions, please let me know. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|