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Concern-specific annotations for finding bugs in Java-like programs

Concern-specific annotations for finding bugs in Java-like programs. Lieven Desmet, Bart Jacobs, Frank Piessens, Jan Smans and Dries Vanoverberghe K.U. Leuven, Belgium Wolfram Schulte Microsoft Research, Redmond. Type systems are great!. lightweight sufficiently expressive decidable

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Concern-specific annotations for finding bugs in Java-like programs

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  1. Concern-specific annotations for finding bugs in Java-like programs Lieven Desmet, Bart Jacobs, Frank Piessens, Jan Smans and Dries Vanoverberghe K.U. Leuven, Belgium Wolfram Schulte Microsoft Research, Redmond

  2. Type systems are great! • lightweight • sufficiently expressive • decidable • fast • modular • the most successful formal method!

  3. Type systems for Java-like languages • concurrency • Type-Based Race Detection for Java Cormac Flanagan, Stephen N. Freund (PLDI 00) • Ownership Types for Safe Programming: Preventing Data Races and Deadlocks Chandrasekhar Boyapati, Robert Lee, Martin Rinard (OOPSLA 02) • encapsulation • Modular Specification and Verification of Object-Oriented Programs Peter Müller, PhD • Simple Loose Ownership DomainsJan Schäfer, Arnd Poetsch-Heffter (FTFJP 06) • non-null • Declaring and checking non-null types in an object-oriented languageK. Rustan M. Leino,Manuel Fähndrich (OOPSLA 03) • security • A systematic approach to static access controlFrançois Pottier, Christian Skalka, Scott Smith(ACM TOPLAS 05) • sessions • Session Types for Object-Oriented LanguagesMariangiola Dezani-Ciancaglini,Dimitris Mostrous, Nobuko Yoshida and Sophia Drossopoulou (FMCO 06) • ... so, lots of type systems that address a specific concern! 

  4. but... • ... how can we combine them in a way they can (re-)use each other’s info? • ... type systems can be too stringent.

  5. Existing practice • type system/concern • type checker/type system • verification ≈ • run type checkers in sequence • advantages: • easy, simple, fast • disadvantages: • hard to (re-)use info from other type systems • more or less fixed expressiveness • mandatory; all or nothing • run-time effects

  6. Our proposal • (optional) annotations/concern • vc generator/annotation • verification ≈ • generate vc condition • use theorem prover • advantages: • info can be reused by multiple concerns • flexible precision • more expressive, less stringent • disadvantages: • slower • too expressive, then undecidable

  7. Three Applications • concurrency-related bugs • Ownership Types for Safe Programming: ...Chandrasekhar Boyapati, Robert Lee, Martin Rinard (OOPSLA 02) • stack inspection-related bugs • A Systematic Approach To Static Access ControlFrançois Pottier, Christian Skalka, Scott Smith(ACM TOPLAS 05) • data dependency-related bugs • for frameworks using a blackboard style repository

  8. Concurrency-related bugs? • data races • deadlocks

  9. Data race class Counter { int dangerous; void Inc() { dangerous++; } } Counter ct = new Counter(); new Thread(ct.Inc).Start(); new Thread(ct.Inc).Start(); //What is the value of the field ct.dangerous? A data race occurs when a shared variable is written by one thread and concurrently read or written by another. How to guarantee there are no data races?

  10. Rules and conceptual model • rule: • A thread t can only access the fields of an object o if either the object is thread-local or t holds o’s lock. • conceptual model: • Each thread has corresponding access set, consisting of all objects it has created but not shared yet or whose lock it holds. • Threads can only access (fields of) objects in their access set. • Prevent data races by ensuring that access sets remain disjoint!

  11. Annotations and ghost state • Threads have access sets. • t.A is a new ghost field per thread describing the set of objects accessible to that thread. • Objects can be shared. • o.shared is a boolean ghost field in each object o • share(o); is new operation that shares an unshared o • Fields can be declared to be shared. • Shared fields can only be assigned shared objects.

  12. Object life cycle acquire free locked new share release unshared shared • A new o is unshared, and added to tid.A. • An unshared o can be made accessible for other threads by sharing it; o is taken out of tid.A • A shared o can be exclusively acquired by locking it; when locking succeeds o is added to tid.A • A locked o can be released for others by unlocking it; o is taken out of tid.A.

  13. Translation to VC’s vc(x := o.f; s, Q) ≡ o  tid.A && vc(s, Q)[H(o, f)/x] vc(share (o); s, Q)≡ o  tid.A && !o.shared && vc(s, Q)[(tid.A\{o})/tid.A, H[o.shared→true]/H] ...

  14. Example for Data Race Freedom class Session { shared Counter c; Session(Counter c) requires c.shared; ensuresthistid.A; ensures !this.shared; { this.c = c; } void Run() requires tid.A == {this}; { lock(this.c) { this.c.x++; } } } Counter c = new Counter(); share(c); Session s = new Session(c); Session s2 = new Session(c); new Thread(s.Run).Start(); new Thread(s2.Run).Start();

  15. Example for Data Race Freedom class Session { shared Counter c; threadlocal Session(sharedCounter c) { this.c = c; } void Run() requires tid.A == {this}; { lock(this.c) { this.c.x++; } } } Counter c = new Counter(); share(c); Session s = new Session(c); Session s2 = new Session(c); new Thread(s.Run).Start(); new Thread(s2.Run).Start();

  16. Deadlock Dining Philosophers 1 has F1, waits for F2 2 has F2, waits for F3 3 has F3, waits for F1 A deadlock occurs when a set of threads each wait for a lock (i.e shared object) that another thread holds. 3 Fork 1 Fork 3 1 2 Fork 2 How to guarantee there are no deadlocks?

  17. Rule • rule: • partial order over all shared objects • each thread must acquire shared objects in descending order

  18. Annotations and ghost state • We construct a partial order on shared objects, called ≺. • When o is shared, we add edges to the partial order as specified in the share command’s where clause. • Each thread has a new ghostfield lockstack, holding the set of acquired locks.

  19. Translation to VC’s vc(share (o) where p<o<q; s, Q)≡ o  tid.A && !o.shared && p≺q && p≺o≺q  vc(s, Q)[(tid.A\{o})/A, H[o.shared→true]/H] vc(lock(o) { B }; s, Q) ≡ o.shared && (tid.lockstack.Empty || o≺tid.lockstack.top) && vc(B; unlock(o);s, Q)[(tid.A\{o})/A, ...]

  20. Example for Deadlock Freedom Fork f1 = new Fork(); share(f1); Fork f2 = new Fork(); share(f2) where f1≺f2; Fork f3 = new Fork(); share(f3) where f2≺f3; new Thread( delegate() {lock (f2) { lock (f1) { /*eat*/ }}} ).Start(); new Thread( delegate() {lock (f3) { lock (f2) { /*eat*/ }}} ).Start(); new Thread( delegate() {lock (f3) { lock (f1) { /*eat*/ }}} ).Start(); 3 left right Fork 1 Fork 3 right left 1 2 right left Fork 2

  21. Comparison with Boyapati • advantages: • support for more complex ownership transfer patterns • disadvantages: • undecidable • slower

  22. Conclusion: concurrency-related bugs • data race freedom • access set per thread • access sets disjoint • deadlock freedom • partial order over shared objects • lock in descending order • A Statically Verifiable Programming Model for Concurrent Object-Oriented ProgramsBart Jacobs, Jan Smans, Frank Piessens, Wolfram Schulte (ICFEM 06) • Safe Concurrency for Aggregate Objects with InvariantsBart Jacobs, K. Rustan M. Leino, Frank Piessens, Wolfram Schulte (SEFM 05)

  23. Stack inspection-related bugs • what is stack inspection? • technology for safely executing untrusted code • how? • at load-time, each component is assigned a static permission set • at run-time, each thread maintains a dynamic permission set • ∩ of static permission sets of methods on the call stack • before sensitive operation, check dynamic permission set (Demand) • if ok, no-op; otherwise, SecurityException

  24. What are stack inspection-related bugs? SecurityExceptions! • similar to Esc/Java’s or Spec#’s treat-ment of NullPointerExceptions

  25. Rule • rule: • invoke a sensitive operation (and the corresponding Demand) only if sufficient permissions are present

  26. Annotations and ghost state • Threads have dynamic permission sets. • t.Dynamic is a new ghost field per thread describing t’s dynamic permission set. • Components have static permission sets. • staticc is a ghost field per class, describing the static permissions associated with that class. • Underspecify static permission sets using the Minimum attributes.

  27. Translation to VC’s* vc_sps(p.Demand(); s, Q)≡ p  tid.Dynamic && vc(s, Q) vc_sps(o.Method(); s, Q) ≡ vc(o.Method(tid.Dynamic);s, Q[...]) for every method body s in a class C: vc_sps(s, Q) ≡ vc(s, Q[(tid.Dynamic ∩ staticC)/tid.Dynamic]) * essentially a Security-passing Style Transformation(Dan S. Wallach)

  28. An example

  29. Example (2) class Assembly{ static Assembly LoadFrom(String url) requires url.StartsWith(“file:”) ==> tid.Dynamic.Contains(new FileIOPermission(url)); requires ! url.StartsWith(“file:”) ==> tid.Dynamic.Contains(new WebPermission()); { if(url.StartsWith(“file:”)){ new FileIOPermission(url).Demand(); //open and return the assembly } else{ new WebPermission().Demand(); //open and return the assembly } } }

  30. Comparison with Pottier • advantages: • path-sensitive • permission parameters • disadvantages: • in general, undecidable • slower

  31. Conclusion: stack inspection-related bugs • SecurityException freedom • keep track of dynamic permission set • Demand only if present • Static Verification of Code Access Security Policy Compliance of .NET Applications • Jan Smans, Bart Jacobs, Frank Piessens (JOT April 06) • Static Verification of Code Access Security Policy Compliance of .NET Applications • Jan Smans, Bart Jacobs, Frank Piessens (.NET Technologies 05)

  32. Data Dependency-related bugs • Static Verification of Indirect Data Sharing in Loosely-coupled Component • Systems • Lieven Desmet, Frank Piessens, Wouter Joosen en Pierre Verbaeten (SC 06) • Bridging the Gap between Web Application Firewalls and • Web Applications • Lieven Desmet, Frank Piessens, Wouter Joosen en Pierre Verbaeten (FMSE 06)

  33. Generalization: a methodology for designing concern-specific annotations • Pick a concern. • Design a set of rules to address the concern. • Decide on the conceptual model. • Decide on the ghost state to be tracked and corresponding annotations. • Define the transformation from annotated programs to VC’s. • Prove soundness.

  34. Examples of reuse • aliasing • method framing • ...

  35. Related Work • similar projects: • Enforcing Resource Bounds via Static Verification of Dynamic Checks (JRes)Ajay Chander, David Espinosa, Nayeem Islam, Peter Lee, George Necula (ESOP 05) • ...

  36. Related Work (2) • Static Typing Where Possible, Dynamic Typing When Needed • Hybrid Type Checking Cormac Flanagan (POPL 06) • Static Typing Where Possible, Dynamic Typing When NeededErik Meijer, Peter Drayton (RDL 04) • Soft TypingRobert Cartwright, Mike Fagan (PLDI 91) • Universes: Lightweight Ownership for JMLWerner Dietl, Peter Müller (JOT 05)

  37. Related Work (3) • Pluggable/Optional Type Systems • Pluggable Type SystemsGilad Bracha (RDL 04) • ...

  38. Future Work • type checking where possible, theorem proving when needed • more case studies • e.g. Java type system?

  39. Conclusion • type systems → verification system • +: more expressive • +: (re)-use of information between concerns • -: slower • -: possibly undecidable • evidence: 3 case studies

  40. Thx for listening! Questions?

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