On Mon, Mar 9, 2015 at 4:40 PM, Daniel De Graaf <[email protected]> wrote:
> 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. I thought of using TPM_PCRRead from virtual machine but it was not clear for me if it is safe. Is it possible for the selected vTPM PCRs values to be different when performing composite hash on vTPM from the values read with TPM_PCRRead after executing DeepQuote? The TPM has context management for each application? (eg: when one application extends something into a PCR and another application extends other thing in the same PCR(at the same time moment), are they hashed together?) When I read the standard I understood that the PCRs can never be overwritten, just reset and extended. Thanks. > > > 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 >
_______________________________________________ Xen-devel mailing list [email protected] http://lists.xen.org/xen-devel
