From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel De Graaf Subject: Re: vTPM Deep Quote validation Date: Mon, 09 Mar 2015 10:40:13 -0400 Message-ID: <54FDB0CD.1080905@tycho.nsa.gov> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Emil Condrea , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 03/08/2015 07:41 AM, Emil Condrea wrote: > I am trying to validate a Deep Quote request made by domU but I feel that > something is missing. Right now when a domU requests TPM_ORD_DeepQuote: > 1. vTPM: > - unpacks the params: nonce, vTPM PCR selection and physical PCR selection > - packs PCR_INFO_SHORT structure into buf that contains the selected vTPM > PCRs > - computes nonce as a SHA1 of: dquot_hdr, nonce, and previous packed buf > - packs: nonce, physical PCR selection > - receives physical pcr data and signature from manager and returns them to > DomU > 2. vTPM Manager > - unpacks the params: nonce, PCR selection > - execute TPM_Quote with: externalData = nonce > - returns pcr data and signature to vTPM > > If domU user wants to validate the signature it has to do the exact process > that the vtpm and manager did but the virtual PCR values are not included > in response, just physical ones. The virtual machine can use TPM_PCRRead to get the value of the vTPM PCRs. This is the same method that is used by the TPM_Quote2 command. > We can include the vTPM PCRS in response or the manager must perform > TPM_Quote using the nonce received from domU in order to be able to have a > successful validation on the client side. If you want a quote without any vTPM PCRs, you can specify an empty PCR mask to get something fairly close to this behavior - the nonce will be combined with an empty deep quote structure instead of passed directly. > What do you think? Is there something that I am missing ? It is useful to be able to ask for the current value of both physical and virtual PCRs in a single atomic operation. Including the value of all PCRs in the response could make the reply packet too large (which is part of the reason why TPM_Quote2 removed them). -- Daniel De Graaf National Security Agency