Source-code verification works by reasoning about the semantics of the full source code of a program. Traditionally it is limited to small programs written in an academic programming language. In this paper we present the VFiasco (Verified Fiasco) project, in which we apply source-code verification to a complete operating-system kernel written in C++. The aim of the VFiasco project is to establish security relevant properties of the Fiasco microkernel using source code verification. The project's main challenges are to develop a clean semantics for the subset of C++ used by the kernel and to enable high-level reasoning about typed data starting from only low-level knowledge about the hardware. In this paper we present our ideas for tackling these challenges. We sketch a semantics of C++ and develop a type-safe object store for reasoning about C++ programs. This object store is based on a hardware model that closely resembles the IA32 virtual-memory architecture, and on guarantees provided by the kernel itself.

Proof-Carrying Code (PCC) and other applications in computer security require machine-checkable proofs of properties of machine-language programs. The main advantage of the PCC approach is that the amount of code that must be explicitly trusted is very small: it consists of the logic in which predicates and proofs are expressed, the safety predicate, and the proof checker. We have built a minimal proof checker, and we explain its design principles, and the representation issues of the logic, safety predicate, and safety proofs. We show that the trusted computing base (TCB) in such a system can indeed be very small. In our current system the TCB is less than 2,700 lines of code (an order of magnitude smaller even than other PCC systems) which adds to our confidence of its correctness.

Typed Assembly Languages (TALs) can be used to validate the safety of assembly-language programs. However, typing rules are usually trusted as axioms.