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We present Copland, a language for specifying layered attestations. Layered attestations provide a remote appraiser with structured evidence of the integrity of a target system to support a trust decision. The language is designed to bridge the gap between formal analysis of attestation security guarantees and concrete implementations. We therefore provide two semantic interpretations of terms in our language. The first is a denotational semantics in terms of partially ordered sets of events. This directly connects Copland to prior work on layered attestation. The second is an operational semantics detailing how the data and control flow are executed. This gives explicit implementation guidance for attestation frameworks. We show a formal connection between the two semantics ensuring that any execution according to the operational semantics is consistent with the denotational event semantics. This ensures that formal guarantees resulting from analyzing the event semantics will hold for executions respecting the operational semantics. All results have been formally verified with the Coq proof assistant.

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Recent work in software integrity verification provides techniques for measuring integrity at runtime, where a measurement agent observes the memory image of a running process and constructs some meaningful description of the process's current state. Unlike in static and load time measurement architectures, the target of a runtime measurement is running and hence able to change its state. In this setting, an accurate measurement must reflect a coherent state of the target. A coherent measurement must satisfy two properties: atomicity ensures that a measurement corresponds to the state of the target at a particular point in time and quiescence ensures that the target data is in a consistent state, i.e. not a critical section. We address the former property, showing that we can obtain an atomic measurement using a memory copy-on-write strategy, which we have implemented in the Xen hypervisor. We show that this approach achieves significant performance gains in the memory and time impact to the target, when compared with naive strategies for enforcing atomicity.