Synthesising correct concurrent runtime monitors

This paper studies the correctness of automated synthesis for concurrent monitors. We adapt a subset of the Hennessy-Milner logic with recursion (a reformulation of the modal μ-calculus) to specify safety properties for Erlang programs. We also define an automated translation from formulas in this sub-logic to concurrent Erlang monitors that detect formula violations at runtime. Subsequently, we formalise a novel definition for monitor correctness that incorporates monitor behaviour when instrumented with the program being monitored. Finally, we devise a sound technique that allows us to prove monitor correctness in stages; this technique is used to prove the correctness of our automated monitor synthesis.peer-reviewe

On Synchronous and Asynchronous Monitor Instrumentation for Actor-based systems

We study the impact of synchronous and asynchronous monitoring instrumentation on runtime overheads in the context of a runtime verification framework for actor-based systems. We show that, in such a context, asynchronous monitoring incurs substantially lower overhead costs. We also show how, for certain properties that require synchronous monitoring, a hybrid approach can be used that ensures timely violation detections for the important events while, at the same time, incurring lower overhead costs that are closer to those of an asynchronous instrumentation.Comment: In Proceedings FOCLASA 2014, arXiv:1502.0315

On Runtime Enforcement via Suppressions

Runtime enforcement is a dynamic analysis technique that uses monitors to enforce the behaviour specified by some correctness property on an executing system. The enforceability of a logic captures the extent to which the properties expressible via the logic can be enforced at runtime. We study the enforceability of Hennessy-Milner Logic with Recursion (muHML) with respect to suppression enforcement. We develop an operational framework for enforcement which we then use to formalise when a monitor enforces a muHML property. We also show that the safety syntactic fragment of the logic, sHML, is enforceable by providing an automated synthesis function that generates correct suppression monitors from sHML formulas

A Foundation for Runtime Monitoring

Runtime Verification is a lightweight technique that complements other verification methods in an effort to ensure software correctness. The technique poses novel questions to software engineers: it is not easy to identify which specifications are amenable to runtime monitoring, nor is it clear which monitors effect the required runtime analysis correctly. This exposition targets a foundational understanding of these questions. Particularly, it considers an expressive specification logic (a syntactic variant of the mmucalc) that is agnostic of the verification method used, together with an elemental framework providing an operational semantics for the runtime analysis performed by monitors. The correspondence between the property satisfactions in the logic on the one hand, and the verdicts reached by the monitors performing the analysis on the other, is a central theme of the study. Such a correspondence underpins the concept of monitorability, used to identify the subsets of the logic that can be adequately monitored for by RV. Another theme of the study is that of understanding what should be expected of a monitor in order for the verification process to be correct. We show how the monitor framework considered can constitute a basis whereby various notions of monitor correctness may be defined and investigated

A foundation for runtime monitoring

Runtime Verification is a lightweight technique that complements other verification methods in an effort to ensure software correctness. The technique poses novel questions to software engineers: it is not easy to identify which specifications are amenable to runtime monitor-ing, nor is it clear which monitors effect the required runtime analysis correctly. This exposition targets a foundational understanding of these questions. Particularly, it considers an expressive specification logic (a syntactic variant of the modal μ-calculus) that is agnostic of the verification method used, together with an elemental framework providing an operational semantics for the runtime analysis performed by monitors. The correspondence between the property satisfactions in the logic on the one hand, and the verdicts reached by the monitors performing the analysis on the other, is a central theme of the study. Such a correspondence underpins the concept of monitorability, used to identify the subsets of the logic that can be adequately monitored for by RV. Another theme of the study is that of understanding what should be expected of a monitor in order for the verification process to be correct. We show how the monitor framework considered can constitute a basis whereby various notions of monitor correctness may be defined and investigated.peer-reviewe

On synchronous and asynchronous monitor instrumentation for actor-based systems

We study the impact of synchronous and asynchronous monitoring instrumentation on runtime overheads in the context of a runtime verification framework for actor-based systems. We show that, in such a context, asynchronous monitoring incurs substantially lower overhead costs. We also show how, for certain properties that require synchronous monitoring, a hybrid approach can be used that ensures timely violation detections for the important events while, at the same time, incurring lower overhead costs that are closer to those of an asynchronous instrumentation.peer-reviewe

Consistently-detecting monitors

We study a contextual definition for deterministic monitoring based on consistent detections. It is defined in terms of the observed behaviour of the monitor when instrumented over arbitrary systems. We give an alternative, coinductive definition based on controllability which does not rely on system quantifications, and show that it is fully-abstract wrt. the former definition. We then develop a symbolic counterpart to the controllability definition to facilitate an automated analysis for controllable monitors involving data.peer-reviewe

Monitoring distributed systems with distributed polyLarva

polyLarva is a language-agnostic runtime verification tool, which converts a polyLarvaScript into a monitor for a given system. While an implementation for polyLarva exists, the language and its compilation have not been formalised. We therefore present a formal implementation-independent model which describes the behaviour of polyLarvaScript, comprising of the uLarvaScript grammar and of a set of operational semantics. This allows us to prove important properties, such as determinism, and also enables us to reason about ways of re-designing the tool in a more scalable way. We also present a collection of denotational mappings for uLarvaScript converting the constructs of our grammar into constructs of a formal actor-based model, thus providing an Actor semantics for uLarvaScript. We are also able to prove certain correctness properties of the denotational translation such as that the denoted Actors behave in a way which corresponds to the behaviour described by our implementation-independent model. We finally present distPolyLarva, a prototype implementation of the distributed polyLarva tool, which implements the new actor-based semantics over a language that can natively handle distribution and concurrency called Erlang.peer-reviewe