Emulated Trusted Platform Module (vTPM)¶
New in version 22.0.0: (Victoria)
Starting in the 22.0.0 (Victoria) release, Nova supports adding an emulated virtual Trusted Platform Module (vTPM) to guests.
The following are required on each compute host wishing to support the vTPM feature:
Currently vTPM is only supported when using the libvirt compute driver with a
libvirt.swtpm_enabledconfig option to
True. This will enable support for both TPM version 1.2 and 2.0.
With the above requirements satisfied, verify vTPM support by inspecting the traits on the compute node’s resource provider:
$ COMPUTE_UUID=$(openstack resource provider list --name $HOST -f value -c uuid) $ openstack resource provider trait list $COMPUTE_UUID | grep SECURITY_TPM | COMPUTE_SECURITY_TPM_1_2 | | COMPUTE_SECURITY_TPM_2_0 |
Configuring a flavor or image¶
A vTPM can be requested on a server via flavor extra specs or image metadata properties. There are two versions supported - 1.2 and 2.0 - and two models - TPM Interface Specification (TIS) and Command-Response Buffer (CRB). The CRB model is only supported with version 2.0.
Specify the TPM version,
Specify the TPM model,
For example, to configure a flavor to use the TPM 2.0 with the CRB model:
$ openstack flavor set $FLAVOR \ --property hw:tpm_version=2.0 \ --property hw:tpm_model=tpm-crb
Scheduling will fail if flavor and image supply conflicting values, or if model
tpm-crb is requested with version
Upon successful boot, the server should see a TPM device such as
which can be used in the same manner as a hardware TPM.
Only server operations performed by the server owner are supported, as the user’s credentials are required to unlock the virtual device files on the host. Thus the admin may need to decide whether to grant the user additional policy roles; if not, those operations are effectively disabled.
Live migration, evacuation, shelving and rescuing of servers with vTPMs is not currently supported.
With a hardware TPM, the root of trust is a secret known only to the TPM user. In contrast, an emulated TPM comprises a file on disk which the libvirt daemon must be able to present to the guest. At rest, this file is encrypted using a passphrase stored in a key manager service. The passphrase in the key manager is associated with the credentials of the owner of the server (the user who initially created it). The passphrase is retrieved and used by libvirt to unlock the emulated TPM data any time the server is booted.
Although the above mechanism uses a libvirt secret that is both
(can’t be displayed via the libvirt API or
only in memory, never on disk), it is theoretically possible for a sufficiently
privileged user to retrieve the secret and/or vTPM data from memory.
A full analysis and discussion of security issues related to emulated TPM is beyond the scope of this document.