Modern computing systems have grown in complexity, and the attack surface has increased accordingly. Even though system components are generally carefully designed and even verified by different groups of people, the composition of these components is often regarded with less attention. This paves the way for "architectural attacks", a class of security vulnerabilities where the attacker is able to threaten the security of the system even if each of its components continues to act as expected. In this article, we introduce FreeSpec, a formalism built upon the key idea that components can be modelled as programs with algebraic effects to be realized by other components. FreeSpec allows for the modular modelling of a complex system, by defining idealized components connected together, and the modular verification of the properties of their composition. In addition, we have implemented a framework for the Coq proof assistant based on FreeSpec. OSApp Execution Unit MMU Cache APIC IOMMU MCH Management Engine DRAM Controller VGA Controller SENTER Sandman [6], SpeedRacer [5] SMRAM cache poisoning [2,3] DMA Attacks [7] Sinkhole [4]

Abstract. Over time, hardware designs have constantly grown in complexity and modern platforms involve multiple interconnected hardware components. During the last decade, several vulnerability disclosures have proven that trust in hardware can be misplaced. In this article, we give a formal definition of Hardware-based Security Enforcement (HSE) mechanisms, a class of security enforcement mechanisms such that a software component relies on the underlying hardware platform to enforce a security policy. We then model a subset of a x86-based hardware platform specifications and we prove the soundness of a realistic HSE mechanism within this model using Coq, a proof assistant system.