模型检测中的偏序约简

检查并发系统的性质变得日益困难。随着验证方法的发展,一些复杂系统并发性越来越高,越来越难以理解。偏序约简方法被提出以减少自动验证并发系统所需要的时间和内存。文中介绍了偏序约简技术的主要概念和基本算法,介绍了其在LTL中的应用,提出了改进方法。     

Formal Verification of a Partial-Order Reduction Technique for Model Checking

Mechanical theorem proving and model checking are the two main methods of formal verification, each with its own strengths and weaknesses. While mechanical theorem proving is more general, it requires intensive human guidance. Model checking is automatic, but is applicable to a more restricted class of problems. It is appealing to combine these two methods in order to take advantage of their different strengths. Prior research in this direction has focused on how to decompose a verification problem into parts each of which is manageable by one of the two methods. In this paper we explore another possibility: we use mechanical theorem proving to formally verify a meta-theory of model checking. As a case study, we use the mechanical theorem prover HOL to verify the correctness of a partial-order reduction technique for cutting down the amount of state search performed by model checkers. We choose this example for two reasons. First, this reduction technique has been implemented in the protocol analysis tool SPIN to significantly speed up the analysis of many practical protocols; hence its correctness has important practical consequences. Second, the correctness arguments involve nontrivial mathematics, the formalization of which we hope will become the basis of a formal meta-theory of other model-checking algorithms and techniques. Interestingly, our formalization led to a nontrivial generalization of the original informal theory. We discuss the lessons, both encouraging and discouraging, learned from this exercise. In the appendix we highlight the important definitions and theorems from each of our HOL theories. The complete listing of our HOL proof is given in a separate document because of space limitations.     

Partial Order Reduction for Verification of Spatial Properties of Pi-Calculus Processes

Mechanical tools have recently been developed that enable computer-aided verification of spatial properties of concurrent systems. To be practical, these tools are expected to deal with the state- space explosion problem. In order to alleviate this problem, we develop partial order reduction for verification of spatial properties of pi-calculus processes. The main issue is that spatial logics are very expressive and some spatial formulas prevent partial order reduction. After discussing this issue, we propose a restricted spatial logic such that partial order reduction holds. Our approach relies on exploiting partially confluent communications and on identifying invisible communications in the pi-calculus, for which we propose a simple syntactic criterion.     

An Efficient Partial Order Reduction Algorithm with an Alternative Proviso Implementation

This paper presents a partial order reduction algorithm called Twophase that generates a significantly reduced state space on a large class of practical protocols over alternative algorithms in its class. The reduced state-space generated by Twophase preserves all CTL*-X assertions. Twophase achieves this reduction by following an alternative implementation of the proviso step. In particular, Twophase avoids the in-stack check that other tools use in order to realize the proviso step. In this paper, we demonstrate that the in-stack check is inefficient in practice, and demonstrate a much simpler alternative method of realizing the proviso. Twophase can be easily combined with an on-the-fly model-checking algorithm to reduce memory requirements further. A simple but powerful selective caching scheme can also be easily added to Twophase.A version of Twophase using on-the-fly model-checking and selective caching has been implemented in a model-checker called PV (Protocol Verifier) and is in routine use on large problems. PV accepts a proper subset of Promela and a never automaton expressing the LTL-X assertion to be verified. PV has helped us complete full state-space search several orders of magnitude faster than all alternative tools available in its class on dozens of real protocols. PV has helped us detect bugs in real Distributed Shared Memory cache coherency protocols that were missed during incomplete search using alternate tools.     

事务级形式验证技术及8051验证模型

提出一种基于事务的用于电路系统的形式验证方法(TBFV)．应用该方法,验证工程师可以在行为级对系统进行验证,无需了解设计的细节．为了对该方法进行示范,验证了8051的RTL级实现,并给出了8051指令集的TBFV模型．     

Relaxed Visibility Enhances Partial Order Reduction

State-space explosion is a central problem in the automatic verification (model-checking) of concurrent systems. Partial order reduction is a method that was developed to try to cope with the state-space explosion. Based on the observation that the order of execution of concurrent (independent) atomic actions is in many cases unimportant for the checked property, it allows reducing the state space by exploring fewer execution sequences. However, in order to guarantee that the reduced state space preserves the correctness of the checked property, the partial order reductions put constraints about commuting the order of atomic actions that may change the value of propositions appearing in the checked specification. In this paper we relax this constraint, allowing a weaker requirement to be imposed, and thus achieving a better reduction. We demonstrate the benefits of our improved reduction with experimental results.     

KRust:Rust形式化可执行语义

Rust是新兴的系统级编程语言,旨在提供内存安全的同时保证极高的性能。Rust形式化语义是用来证明其内存安全和开发Rust程序分析工具的基础。鉴于目前没有直接描述Rust的形式化语义,提出了针对Rust语言的形式化可执行语义KRust。为了确保语义的可执行性和应用性,使用了K框架进行语义的开发。KRust目前涵盖了Rust常见的语法和语义,包括了Rust的3个核心特性:所有权、借用和生命周期。KRust通过了191个测试样例,其中157个都是来自Rust官方的测试集。语义对比测试实验发现了Rust编译器的缺陷。此外,KRust的语义还可以被应用于开发Rust程序分析工具。     

Distributed Partial Order Reduction of State Spaces

State space explosion is a fundamental obstacle in formal verification of concurrent systems. Several techniques for combating this problem have emerged in the past few years, among which the two we are interested in are: partial order reduction and distributed memory state exploration. While the first one tries to reduce the problem to a smaller one, the other one tries to extend the computational power to solve the same problem. In this paper, we consider a combination of these two approaches and propose a distributed memory algorithm for partial order reduction.     

Verification of synchronous-automaton programs with the use of LTL

A way to verify synchronous-automaton programs using the language of linear-time temporal logic with past-tense operators is proposed. The employment of the TempEst software tool is studied. The specification and checking of the properties are illustrated using the example of an alarm clock.     

Distributed Partial Order Reduction for Security Protocols

We describe a distributed partial order reduction algorithm for security protocols. Some experimental results using an implementation of the algorithm in the distributed μCRL toolset are also reported.     

Partial Order Reduction for Probabilistic Branching Time

In the past, partial order reduction has been used successfully to combat the state explosion problem in the context of model checking for non-probabilistic systems. For both linear time and branching time specifications, methods have been developed to apply partial order reduction in the context of model checking. Only recently, results were published that give criteria on applying partial order reduction for verifying quantitative linear time properties for probabilistic systems. This paper presents partial order reduction criteria for Markov decision processes and branching time properties, such as formulas of probabilistic computation tree logic. Moreover, we provide a comparison of the results established so far about reduction conditions for Markov decision processes.     

偏序关系在形式概念分析中的应用

将偏序关系应用到形式概念分析中,定义了三个基于偏序集的衍生形式背景,利用衍生形式背景对原形式背景中的概念、内涵、可约对象、可约属性及蕴含规则进行了刻画,这种刻画更有利于人们对形式概念分析的深入理解。     

BLP改进模型的形式化描述及自动化验证

在《信息安全技术操作系统安全技术要求》中,提出访问验证保护级安全操作系统的研发过程需要完全形式化的安全策略模型。针对该情况,对经典的数据机密性BLP模型进行相应改进,为系统中的主客体引入多级安全标签以及安全迁移规则,使其满足实际系统开发的需求。运用完全形式化的方法对改进模型的状态、不变量、迁移规则等进行描述,使用Isabelle定理证明器证明了迁移规则对模型的不变量保持性,从而实现对模型正确性的自动形式化验证,并保证了模型的可靠性。     

基于Rebeca模型的硬件设计形式化验证

形式化验证是对传统验证方法的补充,是数字电路验证的一条有效途径,对于并发系统,行为建模是一种非常合适的建模方法;Rebeca是由Sirjani和Movaghar提出的一种基于行为的建模语言,支持形式化,一方面,Rebeca是一种类Java的语言,软件工程师很容易使用,另一方面,它是一种支持形式化验证及其相关理论的模型语言,可以为不精通于形式化方法的开发人员和研究人员提供方便的验证过程;在深入研究Rebeca的基础上,采用Rebeca对硬件设计进行建模,然后Modere形式化验证工具对AES密码芯片进行形式化验证。     

Formal Verification of a Railway Interlocking System using Model Checking

In this paper we describe an industrial application of formal methods. We have used model checking techniques to model and formally verify a rather complex software, i.e. part of the “safety logic” of a railway interlocking system. The formal model is structured to retain the reusability and scalability properties of the system being modelled. Part of it is defined once for all at a low cost, and re-used. The rest of the model can be mechanically generated from the designers' current specification language. The model checker is “hidden” to the user, it runs as a powerful debugger. Its performances are impressive: exhaustive analysis of quite complex configurations with respect to rather complex properties are run in the order of minutes. The main reason for this achievement is essentially a carefully designed model, which exploits all the behaviour evolution constraints. The re-usability/scalability of the model and the fact that formal verification is automatic and efficient are the key factors which open up the possibility of a real usage by designers at design time. We have thus assessed the possibility of introducing the novel technique in the development cycle with an advantageous costs/benefits relation. Received March 1997 / Accepted in revised form July 1998     

基于STP方法的SCADE模型形式化验证框架

高安全性应用开发环境(SCADE)的形式化验证组件Design Verifier能够验证航空航天领域嵌入式软件系统的安全性质,但不能充分描述拥有复杂时序性质的安全需求。为解决该问题,构建一种SCADE状态机的时序性质验证框架,将SCADE模型转换成NuSMV模型,并将线性时态逻辑和计算树逻辑引入SCADE模型的需求规范中。分析结果表明,借助NuSMV模型检查器及其验证结果可检验复杂时序相关的安全性质,减少模型设计阶段的错误,提高系统的安全性和可靠性。     

Formal Verification of Websites

In this paper, a model for websites is presented. The model is well-suited for the formal verification of dynamic as well as static properties of the system. A website is defined as a collection of web pages which are semantically connected in some way. External web pages (which are related pages not belonging to the website) are treated as the environment of the system. We also present the logic which is used to specify properties of websites, and illustrate the kinds of properties that can be specified and verified by using a model-checking tool on the system. In this setting, we discuss some interesting properties which often need to be checked when designing websites. We have encoded the model using the specification language Maude which allows us to use the Maude model-checking tool.     

基于图归约法的工作流模型验证

详细论述了对基于有向有环图（DCG图）的工作流模型结构正确性进行验证的图归约法及其五种归约规则,根据这些规则即可判定工作流模型中存在的结构冲突,从而迅速对其进行修正。