Building Reliable and Secure Virtual Machines using Architectural Invariants

Reliability and security tend to be treated separately because they appear orthogonal: reliability focuses on accidental failures, security on intentional attacks. Because of the apparent dissimilarity between the two, tools to detect and recover from different classes of failures and attacks are usually designed and implemented differently. So, integrating support for reliability and security in a single framework is a significant challenge.

Here, we discuss how to address this challenge in the context of cloud computing, for which reliability and security are growing concerns. Because cloud deployments usually consist of commodity hardware and software, efficient monitoring is key to achieving resiliency. Although reliability and security monitoring might use different types of analytics, the same sensing infrastructure can provide inputs to monitoring modules.

We split monitoring into two phases: logging and auditing. Logging captures data or events; it constitutes the framework's core and is common to all monitors. Auditing analyzes data or events; it's implemented and operated independently by each monitor. To support a range of auditing policies, logging must capture a complete view, including both actions and states of target systems. It must also provide useful, trustworthy information regarding the captured view.

We applied these principles when designing HyperTap, a hypervisor-level monitoring framework for virtual machines (VMs). Unlike most VM-monitoring techniques, HyperTap employs hardware architectural invariants (hardware invariants, for short) to establish the root of trust for logging. Hardware invariants are properties defined and enforced by a hardware platform (for example, the x86 instruction set architecture). Additionally, HyperTap supports continuous, event-driven VM monitoring, which enables both capturing the system state and responding rapidly to actions of interest.