From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============8136628059790980374==" MIME-Version: 1.0 From: Stefan Berger Subject: Re: [tpm2] [Qemu-devel] Choosing PCR banks for swtpm's TPM 2 Date: Mon, 25 Jun 2018 11:56:24 -0400 Message-ID: <6adb28e6-85eb-38dc-ad24-99a5daa0f972@linux.vnet.ibm.com> In-Reply-To: 20180625152513.GI18580@redhat.com List-ID: To: tpm2@lists.01.org --===============8136628059790980374== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On 06/25/2018 11:25 AM, Daniel P. Berrang=C3=A9 wrote: > On Mon, Jun 25, 2018 at 11:05:55AM -0400, Stefan Berger wrote: >> Hi! >> >> =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 measure= ment >> architecture is used and has to extend measurements into all PCR banks, >> which Linux does already. >> >> 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 ha= s to >> be done through the firmware and has the downside that the TPM2 does not >> support TPM2_Shutdown(SU_STATE) after this command was used. This preven= ts >> suspend/resume from working properly. So, it seems that one shouldn't ha= ve >> to use this command, which in turn means the number of PCR banks should = be >> small. >> >> Another complication with the swtpm is the upgrade path. Suspended VMs w= ill >> expect that the PCR banks that were available before the suspend will be >> available after the resume and a possible swtpm upgrade. This in turn me= ans >> that the PCR banks should be chosen now and we'll have to stick with the= m. > Anything that has a risk of needing to change between versions would need > to be tied into the machine type in some way. You mean a machine type like q35? I am not sure how it would be tied = into QEMU since the swtpm command line options are chosen more or less = independently of the ones from QEMU. =C2=A0=C2=A0=C2=A0 Stefan --===============8136628059790980374==--