Open Stack

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Trusted VM can be powered on untrusted hosts
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### Summary ###
A trusted VM that has been launched earlier on a trusted host can
still be powered on from the same host even after the trusted host is
compromised.

### Affected Services / Software ###
Nova, Trusted Computing Pools

### Discussion ###
Trusted Computing Pools aim to ensure the trustworthiness of the hosts
leveraging hardware-based security features. When an instance is
scheduled, the scheduler finds a trusted host by calling the remote
Attestation API for each host to check whether it is trusted or not.
Then, the scheduler calls the corresponding compute node to launch
the VM. Once the VM is launched, the scheduler is no longer involved
unless a migration, a resize or an evacuation is asked for that VM.

Malicious users can bypass the trust check by the Attestation API using
these steps: 1) Launch a trusted VM on a trusted host; 2) Stop the
VM on the trusted host; 3) Compromise the host; 4) Power on the VM from
the compromised host. There is no check by the Attestation API for
powering on the VM in this case.

### Recommended Actions ###
We recommend investigating further if the trust check by Attestation
API fails but the VM still boots. Another approach is to combine
secure boot with trusted boot. At the same time, Nova team has
discussed deprecating Trusted Filter.

### Contacts / References ###
This OSSN : https://wiki.openstack.org/wiki/OSSN/OSSN-0059
Original LaunchPad Bug : https://bugs.launchpad.net/nova/+bug/1456228
OpenStack Security ML : openstack-security at lists.openstack.org
OpenStack Security Group : https://launchpad.net/~openstack-ossg
Nova Team Email Proposing Deprecation:
http://lists.openstack.org/pipermail/openstack-dev/2015-June/067766.html
CR Demoting TrustedFilter to "experimental":
https://review.openstack.org/#/c/194592
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