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The Trusted Virtual Machine Launch Usage Model

A trusted platform boot capability provides a safe launch environment for provisioning virtual machines running workloads. This environment has the mechanisms to evaluate the integrity of pre-launch and launch components on a platform, from the BIOS to the operating system and hypervisor. The service provider thus attests to the trust-ability of the launch environment. However, no specific claims can be made about the virtual machines being launched, other than indicating that they are being launched on a measured and attested hypervisor platform. Although virtual machine monitors (VMM) or hypervisors are naturally good at isolating workloads from each other because they mediate all access to physical resources by virtual machines, they cannot by themselves attest and assert the state of the virtual machine that is launched.

The trusted virtual machine launch usage model applies the same level of trustability to the pre-launch and launch environment of the virtual machines and workloads. Each virtual machine launched on a virtual machine manager and hypervisor platform benefits from a hardware root of trust by storing the launch measurements of the virtual machines' sealing and remote attestation capabilities. However, this requires virtualizing the TPM, with a virtual TPM (vTPM) for each of the virtual machines. Each of these virtual TPM vTPM instances then emulates the functions of a hardware TPM. Currently, there are no real virtualized TPM implementations available, owing to the challenges related to virtualizing the TPM. The difficulty lies not in providing the low-level TPM instructions but in ensuring that the security properties are supported and established with an appropriate level of trust. Specifically, we have to extend the chain of trust from the physical TPM to each virtual TPM by carefully managing the signing keys, certificates, and lifecycle of all necessary elements. An added dimension is the mobility of the virtual machines and how these virtual TPMs would migrate with the virtual machines.

There are other ways of enabling a measured launch of virtual machines, such as storing the measurements in memory as part of a trusted hypervisor platform without the use of virtual TPMs but still ensuring that the chain of trust is extended from the physical TPM. Irrespective of the design approach, day-to-day operations on virtual

machines—such as suspend and resume, creating snapshots of running virtual machines, and playing them back on other platforms or live migration of virtual machines—become challenging to implement.

There are no real production-quality implementations of these architectures. There are few academic and research implementations of vTPMs and other memory structure–based approaches, each with its own pros and cons. Trusted virtual machine usages are still evolving at the time of this writing; hence it's not possible to be definitive. Chapter 8 covers aspects of the measured VM launch and some architectural elements. Chapter 3 covers in depth the matter of boot integrity and trusted boot of platforms and the hypervisors, as well as the associated trusted compute pools concept that aggregates systems so specific policies can be applied to those pools. The discussion also includes the solution architecture, and a snapshot of industry efforts to support the enabling of trusted compute pools. Chapter 4 covers the trust attestation or remote attestation architecture, including a reference implementation.

 
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