Formal verification of a real-time operating system
Errors caused by the interaction of computer systems with the physical world are hard to mitigate but errors related to the underlying software can be prevented by a more rigorous development of software code. In the context of critical systems, a failure caused by software errors could lead to consequences that are determined to be unacceptable. At the heart of a critical system, a real-time operating system is commonly found. Since the reliability of the entire system depends upon having a reliable operating system, verifying that the operating systems functions as desired is of prime interest. One solution to verify the correctness of significant properties of an existing real-time operating system microkernel (FreeRTOS) applies assisted proof checking to its formalized specification description. The experiment consists of describing real-time operating system characteristics, such as memory safety and scheduler determinism, in Separation Logic — a formal language that allows reasoning about the behaviour of the system in terms of preconditions and postconditions. Once the desired properties are defined in a formal language, a theorem can be constructed to describe the validity of such formula for the given FreeRTOS implementation. Then, by using the Coq proof assistant, a machine-checked proof that such properties hold for FreeRTOS can be carried out. By expressing safety and deterministic properties of an existing real-time operating systems and proving them correct we demonstrate that the current state-of-the-art in theorem-based formal verification, including appropriate logics and proof assistants, make it possible to provide a machine-checked proof of the specification of significant properties for FreeRTOS.
Formal Verification, FreeRTOS, Real-Time Operating System, Separation Logic, Coq, Compcert
Master of Science (M.Sc.)