Re: [Xen-devel] [PATCH 1/7] vtpmmgr: add TPM group support

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-03-19 at 15:52 -0400, Daniel De Graaf wrote:
> This is a complete rewrite of the disk format and key hierarchy for the
> TPM Manager. The new format supports multiple groups of vTPMs which
> define the permitted configurations where a given vTPM's keys are
> available, allowing upgrades of critical components while retaining the
> secrecy of cryptographic keys.
> 
> New features of the TPM Manager are explained in the README and in the
> definitions of the management commands in vtpm_manager.h.
> 
> New features for vTPMs:
> 
> 1. The size of the state blob for a vTPM is expanded from 52 to 64
> bytes in order to support future vTPMs using SHA-2/3 instead of SHA-1.
> 
> 2. vTPMs can obtain a quote from the physical TPM with certain
> resettable PCRs set to include information about the vTPM. This can be
> used by a vTPM to provide evidence of its integrity, including the
> secrecy of its EK, and for deep quotes.
> 
> Some additional changes made by this rewrite that may impact existing
> users:
> 
> 1. The value of WELLKNOWN_OWNER_AUTH was incorrect for the physical TPM;
> the convention is to use all zero bits for well-known authentication
> values, not all one bits.
> 
> 2. Randomly generating the owner auth value for the physical TPM is no
> longer supported, as it prevents later creation or certification of
> AIKs (which the old manager did not support).
> 
> 3. The vTPM Manager needs to be provisioned with a PCR composite and an
> upgrade authority's public key before it will save data across boots.
> 
> The current implementation still has some limitations:
>  * 5 valid system PCR selections per group
>  * The vTPM Manager's disk can use at most 2MB of space
>  * The vTPM domain's build hash is always set to null/zero
> 
> Most of the code relating to upgrade and rollback protection is
> currently stubbed out, but future versions can add:
>  * Support for using the TPM's monotonic counter to prevent rollback
>    of vTPM data by taking and restoring disk snapshots
>  * Masking the master disk encryption key using a value stored in the
>    TPM's NVRAM so that revocation of old data is possible without
>    relying on all previously authorized software stacks to respect the
>    monotonic counter's value
> 
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>

As discussed on the previous version I've not extensively reviewed but I
think this should go in nonetheless:

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Ian.


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