Re: [Xen-devel] [PATCH 11/12] vTPM/TPM2: Bind group keys and sectors data on disk

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 12/14/2014 07:09 AM, Quan Xu wrote:
[...]
> +        /*TPM 2.0 bind | TPM 1.x seal*/
> +        if (hw_is_tpm2()) {
> +            TPM2_disk_bind(dst, &sblob, sizeof(sblob));
> +        } else {
> +            dst->pcr_selection = src->seals[i].pcr_selection;
> +            memcpy(&dst->digest_release, &src->seals[i].digest_release, 20);
> +            TPM_pcr_digest(&dst->digest_at_seal, dst->pcr_selection);
> +            TPM_disk_seal(dst, &sblob, sizeof(sblob));
> +        }
It appears that the secrets for the vTPMs are only being bound to the
presence of the physical TPM and not the measurements of the hypervisor
and other TCB components.  This does not provide as much security as it
did for TPM 1.2: an attacker with access to the boot disk can boot into
a compromised environment and extract the vTPM keys and disk images.

The TPM2_Create/TPM2_Unseal operations should be capable of performing
the same functionality.  If only SHA1 PCRs are used, they should be able
to be drop-in replacements, but supporting other hash algorithms may be
a feature that users who have a TPM2 will want.

--
Daniel De Graaf
National Security Agency

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