81 research outputs found
Strong Induction in Hardware Model Checking
Symbolic Model checking is a widely used technique for automated verification of both hardware and software systems. Unbounded SAT-based Symbolic Model Checking (SMC) algorithms are very popular in hardware verification. The principle of strong induction is one of the first techniques for SMC. While elegant and simple to apply, properties as such can rarely be proven using strong induction and when they can be strengthened, there is no effective strategy to guess the depth of induction. It has been mostly displaced by techniques that compute inductive strengthenings based on interpolation and property directed reachability (PDR). In this thesis, we prove that strong induction is more concise than induction. We then present kAvy, an SMC algorithm that effectively uses strong induction to guide interpolation and PDR-style incremental inductive invariant construction. Unlike pure strong induction, kAvy uses PDR-style generalization to compute and strengthen an inductive trace. Unlike pure PDR, kAvy uses relative strong induction to construct an inductive invariant. The depth of induction is adjusted dynamically by minimizing a proof of unsatisfiability. We have implemented kAvy within the Avy Model Checker and evaluated it on HWMCC instances. Our results show that kAvy is more effective than both Avy and PDR, and that using strong induction leads to faster running time and solving more instances. Further, on a class of benchmarks, called shift, kAvy is orders of magnitude faster than Avy, PDR and pure strong induction
CadiBack: Extracting Backbones with CaDiCaL
The backbone of a satisfiable formula is the set of literals that are true in all its satisfying assignments. Backbone computation can improve a wide range of SAT-based applications, such as verification, fault localization and product configuration. In this tool paper, we introduce a new backbone extraction tool called CadiBack. It takes advantage of unique features available in our state-of-the-art SAT solver CaDiCaL including transparent inprocessing and single clause assumptions, which have not been evaluated in this context before. In addition, CaDiCaL is enhanced with an improved algorithm to support model rotation by utilizing watched literal data structures. In our comprehensive experiments with a large number of benchmarks, CadiBack solves 60% more instances than the state-of-the-art backbone extraction tool MiniBones. Our tool is thoroughly tested with fuzzing, internal correctness checking and cross-checking on a large benchmark set. It is publicly available as open source, well documented and easy to extend
Proceedings of the 21st Conference on Formal Methods in Computer-Aided Design – FMCAD 2021
The Conference on Formal Methods in Computer-Aided Design (FMCAD) is an annual conference on the theory and applications of formal methods in hardware and system verification. FMCAD provides a leading forum to researchers in academia and industry for presenting and discussing groundbreaking methods, technologies, theoretical results, and tools for reasoning formally about computing systems. FMCAD covers formal aspects of computer-aided system design including verification, specification, synthesis, and testing
Model-Checking Speculation-Dependent Security Properties: Abstracting and Reducing Processor Models for Sound and Complete Verification
Spectre and Meltdown attacks in modern microprocessors represent a new class of attacks that have been difficult to deal with. They underline vulnerabilities in hardware design that have been going unnoticed for years. This shows the weakness of the state-of-the-art verification process and design practices. These attacks are OS-independent, and they do not exploit any software vulnerabilities. Moreover, they violate all security assumptions ensured by standard security procedures, (e.g., address space isolation), and, as a result, every security mechanism built upon these guarantees. These vulnerabilities allow the attacker to retrieve leaked data without accessing the secret directly. Indeed, they make use of covert channels, which are mechanisms of hidden communication that convey sensitive information without any visible information flow between the malicious party and the victim. The root cause of this type of side-channel attacks lies within the speculative and out-of-order execution of modern high-performance microarchitectures. Since modern processors are hard to verify with standard formal verification techniques, we present a methodology that shows how to transform a realistic model of a speculative and out-of-order processor into an abstract one. Following related formal verification approaches, we simplify the model under consideration by abstraction and refinement steps. We also present an approach to formally verify the abstract model using a standard model checker. The theoretical flow, reliant on established formal verification results, is introduced and a sketch of proof is provided for soundness and correctness. Finally, we demonstrate the feasibility of our approach, by applying it on a pipelined DLX RISC-inspired processor architecture. We show preliminary experimental results to support our claim, performing Bounded Model-Checking with a state-of-the-art model checker
Parameterized Synthesis with Safety Properties
Parameterized synthesis offers a solution to the problem of constructing
correct and verified controllers for parameterized systems. Such systems occur
naturally in practice (e.g., in the form of distributed protocols where the
amount of processes is often unknown at design time and the protocol must work
regardless of the number of processes). In this paper, we present a novel
learning based approach to the synthesis of reactive controllers for
parameterized systems from safety specifications. We use the framework of
regular model checking to model the synthesis problem as an infinite-duration
two-player game and show how one can utilize Angluin's well-known L* algorithm
to learn correct-by-design controllers. This approach results in a synthesis
procedure that is conceptually simpler than existing synthesis methods with a
completeness guarantee, whenever a winning strategy can be expressed by a
regular set. We have implemented our algorithm in a tool called L*-PSynth and
have demonstrated its performance on a range of benchmarks, including robotic
motion planning and distributed protocols. Despite the simplicity of L*-PSynth
it competes well against (and in many cases even outperforms) the
state-of-the-art tools for synthesizing parameterized systems.Comment: 18 page
Proceedings of the 22nd Conference on Formal Methods in Computer-Aided Design – FMCAD 2022
The Conference on Formal Methods in Computer-Aided Design (FMCAD) is an annual conference on the theory and applications of formal methods in hardware and system verification. FMCAD provides a leading forum to researchers in academia and industry for presenting and discussing groundbreaking methods, technologies, theoretical results, and tools for reasoning formally about computing systems. FMCAD covers formal aspects of computer-aided system design including verification, specification, synthesis, and testing
Regular Methods for Operator Precedence Languages
The operator precedence languages (OPLs) represent the largest known subclass of the context-free languages which enjoys all desirable closure and decidability properties. This includes the decidability of language inclusion, which is the ultimate verification problem. Operator precedence grammars, automata, and logics have been investigated and used, for example, to verify programs with arithmetic expressions and exceptions (both of which are deterministic pushdown but lie outside the scope of the visibly pushdown languages). In this paper, we complete the picture and give, for the first time, an algebraic characterization of the class of OPLs in the form of a syntactic congruence that has finitely many equivalence classes exactly for the operator precedence languages. This is a generalization of the celebrated Myhill-Nerode theorem for the regular languages to OPLs. As one of the consequences, we show that universality and language inclusion for nondeterministic operator precedence automata can be solved by an antichain algorithm. Antichain algorithms avoid determinization and complementation through an explicit subset construction, by leveraging a quasi-order on words, which allows the pruning of the search space for counterexample words without sacrificing completeness. Antichain algorithms can be implemented symbolically, and these implementations are today the best-performing algorithms in practice for the inclusion of finite automata. We give a generic construction of the quasi-order needed for antichain algorithms from a finite syntactic congruence. This yields the first antichain algorithm for OPLs, an algorithm that solves the ExpTime-hard language inclusion problem for OPLs in exponential time
RustHorn: CHC-based Verification for Rust Programs (full version)
Reduction to the satisfiability problem for constrained Horn clauses (CHCs)
is a widely studied approach to automated program verification. The current
CHC-based methods for pointer-manipulating programs, however, are not very
scalable. This paper proposes a novel translation of pointer-manipulating Rust
programs into CHCs, which clears away pointers and memories by leveraging
ownership. We formalize the translation for a simplified core of Rust and prove
its correctness. We have implemented a prototype verifier for a subset of Rust
and confirmed the effectiveness of our method.Comment: Full version of the same-titled paper in ESOP202
Proceedings of the 22nd Conference on Formal Methods in Computer-Aided Design – FMCAD 2022
The Conference on Formal Methods in Computer-Aided Design (FMCAD) is an annual conference on the theory and applications of formal methods in hardware and system verification. FMCAD provides a leading forum to researchers in academia and industry for presenting and discussing groundbreaking methods, technologies, theoretical results, and tools for reasoning formally about computing systems. FMCAD covers formal aspects of computer-aided system design including verification, specification, synthesis, and testing
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