Software Model Checking with Explicit Scheduler and Symbolic Threads

In many practical application domains, the software is organized into a set of threads, whose activation is exclusive and controlled by a cooperative scheduling policy: threads execute, without any interruption, until they either terminate or yield the control explicitly to the scheduler. The formal verification of such software poses significant challenges. On the one side, each thread may have infinite state space, and might call for abstraction. On the other side, the scheduling policy is often important for correctness, and an approach based on abstracting the scheduler may result in loss of precision and false positives. Unfortunately, the translation of the problem into a purely sequential software model checking problem turns out to be highly inefficient for the available technologies. We propose a software model checking technique that exploits the intrinsic structure of these programs. Each thread is translated into a separate sequential program and explored symbolically with lazy abstraction, while the overall verification is orchestrated by the direct execution of the scheduler. The approach is optimized by filtering the exploration of the scheduler with the integration of partial-order reduction. The technique, called ESST (Explicit Scheduler, Symbolic Threads) has been implemented and experimentally evaluated on a significant set of benchmarks. The results demonstrate that ESST technique is way more effective than software model checking applied to the sequentialized programs, and that partial-order reduction can lead to further performance improvements.Comment: 40 pages, 10 figures, accepted for publication in journal of logical methods in computer scienc

Certification of Smart-Card Applications in Common Criteria -- Proving Representation Correspondences

We present a method for proving representation correspondences in the Common Criteria (CC) certification of smart-card applications. For security policy enforcement, the CC defines a chain of requirements: a security policy model (SPM), a functional specification (FSP), and a target-of-evaluation design (TDS). In our approach to the CC certification, these requirements are models of applications that can have different representations. A representation correspondence (RCR) describes a correlation between the representations of two adjacent requirements. One task in the CC certification is to demonstrate formal proofs of RCRs. We first develop a modelling framework by which the representations of SPM, FSP and TDS can be described uniformly as models of an application. We then define RCRs as mutual simulations between two application models over sets of observable events and variables. We describe a proof technique for proving RCRs and providing certificates about them based on assertions relating two models at specific locations. We show how RCRs can help us prove property preservation from the SPM to the FSP and the TDS

Inter-Program Properties

We develop foundations for proving properties relating two programs. Our formalization is based on a suitably adapted notion of program invariant for a single program. First, we give an abstract formulation of the theory of program invariants based on the notion of assertion function: a function that assigns assertions to program points. Then, we develop this abstract notion further so that it can be used to prove properties between two programs. We describe an application of the theory to proving program properties in translation validation

Software Model Checking with Explicit Scheduler and Symbolic Threads

In many practical application domains, the software is organized into a set of threads, whose activation is exclusive and controlled by a cooperative scheduling policy: threads execute, without any interruption, until they either terminate or yield the control explicitly to the scheduler. The formal verification of such software poses significant challenges. On the one side, each thread may have infinite state space, and might call for abstraction. On the other side, the scheduling policy is often important for correctness, and an approach based on abstracting the scheduler may result in loss of precision and false positives. Unfortunately, the translation of the problem into a purely sequential software model checking problem turns out to be highly inefficient for the available technologies. We propose a software model checking technique that exploits the intrinsic structure of these programs. Each thread is translated into a separate sequential program and explored symbolically with lazy abstraction, while the overall verification is orchestrated by the direct execution of the scheduler. The approach is optimized by filtering the exploration of the scheduler with the integration of partial-order reduction. The technique, called ESST (Explicit Scheduler, Symbolic Threads) has been implemented and experimentally evaluated on a significant set of benchmarks. The results demonstrate that ESST technique is way more effective than software model checking applied to the sequentialized programs, and that partial-order reduction can lead to further performance improvements