The combination of a hardware-based root of trust such as the Trusted Platform Module (TPM) [23], and a virtual machine-based system such as Xen [4], VMware [26], or PHYP [14], is exceedingly well suited to satisfying these security requirements. Virtual machine monitors, or hypervisors, are naturally good at isolating workloads from each other because they mediate all access to physical resources by virtual machines. A hardware root of trust is resistant to software attacks andprovides a basis for reasoning about the integrity of all software running on a platform, from the hypervisor itself to all operating systems and applications running inside virtual machines.