Concurrent abstraction layers are ubiquitous in modern computer systems because of the pervasiveness of multithreaded programming and multicore hardware. Abstraction layers are used to hide the implementation details (e.g., fine-grained synchronization) and reduce the complex dependencies among components at different levels of abstraction. Despite their obvious importance, concurrent abstraction layers have not been treated formally. This severely limits the applicability of layer-based techniques and makes it difficult to scale verification across multiple concurrent layers.

An operating system (OS) kernel forms the lowest level of any system software stack. The correctness of the OS kernel is the basis for the correctness of the entire system. Recent efforts have demonstrated the feasibility of building formally verified general-purpose kernels, but it is unclear how to extend their work to verify the functional correctness of device drivers, due to the non-local effects of interrupts. In this paper, we present a novel compositional framework for building certified interruptible OS kernels with device drivers. We provide a general device model that can be instantiated with various hardware devices, and a realistic formal model of interrupts, which can be used to reason about interruptible code. We have realized this framework in the Coq proof assistant. To demonstrate the effectiveness of our new approach, we have successfully extended an existing verified non-interruptible kernel with our framework and turned it into an interruptible kernel with verified device drivers. To the best of our knowledge, this is the first verified interruptible operating system with device drivers.

Modern computer systems consist of a multitude of abstraction layers (e.g., OS kernels, hypervisors, device drivers, network protocols), each of which defines an interface that hides the implementation details of a particular set of functionality. Client programs built on top of each layer can be understood solely based on the interface, independent of the layer implementation. Despite their obvious importance, abstraction layers have mostly been treated as a system concept; they have almost never been formally specified or verified. This makes it difficult to establish strong correctness properties, and to scale program verification across multiple layers.