Download
software verification with blast n.
Skip this Video
Loading SlideShow in 5 Seconds..
Software Verification with BLAST PowerPoint Presentation
Download Presentation
Software Verification with BLAST

Software Verification with BLAST

138 Views Download Presentation
Download Presentation

Software Verification with BLAST

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Software Verification withBLAST Tom Henzinger Ranjit Jhala Rupak Majumdar

  2. Blast Web Site http://www.eecs.berkeley.edu/~blast

  3. Software Validation • Large scale reliable software is hard to build and test • Different groups write different components • Integration testing is a nightmare

  4. Property Checking • Programmer gives partial specifications • Code checked for consistency w/ spec • Different from program correctness • Specifications are not complete • Is there a complete spec for Word ? Emacs ?

  5. Interface Usage Rules • Rules in documentation • Order of operations & data access • Resource management • Incomplete, unenforced, wordy • Violated rules ) bad behavior • System crash or deadlock • Unexpected exceptions • Failed runtime checks

  6. lock unlock unlock lock Property 1: Double Locking “An attempt to re-acquire an acquired lock or release a released lock will cause a deadlock.” Calls to lock and unlock must alternate.

  7. Property 2: Drop Root Privilege [Chen-Dean-Wagner ’02] “User applications must not run with root privilege” When execv is called, must have suid  0

  8. start NP CallDriver SKIP1 SKIP2 return child status Skip CallDriver IPC synch MPR3 NP CallDriver prop completion PPC not pending returned MPR completion Complete request CallDriver MPR1 MPR2 DC return not Pend no prop completion synch CallDriver N/A N/A IRP accessible CallDriver start P SKIP2 Mark Pending SKIP1 Skip CallDriver IPC synch MPR3 NP CallDriver prop completion return Pending PPC not pending returned MPR completion Complete request CallDriver MPR1 MPR2 DC no prop completion CallDriver N/A Property 3 : IRP Handler [Fahndrich]

  9. Does a given usage rule hold? • Undecidable! • Equivalent to the halting problem • Restricted computable versions are prohibitively expensive (PSPACE) • Why bother ? • Just because a problem is undecidable, it doesn’t go away!

  10. Plan • Motivation • Lazy Abstraction • Demo • Technical Details

  11. lock unlock unlock lock Example Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4: } while(new != old); 5: unlock (); return; }

  12. pc lock old new q  3   5  5  0x133a pc lock old new q  4   5  6  0x133a What a program really is… State Transition 3: unlock(); new++; 4:} … Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4: } while(new != old); 5: unlock (); return;}

  13. The Safety Verification Problem Error Safe Initial Is there a path from an initial to an error state ? Problem:Infinitestate graph Solution : Set of states ' logical formula

  14. Representing States asFormulas [F] states satisfyingF {s | s² F } F FO fmla over prog. vars [F1] Å [F2] F1ÆF2 [F1] [ [F2] F1 ÇF2 [F] : F [F1] µ [F2] F1 implies F2 i.e. F1Æ: F2 unsatisfiable

  15. Idea 1: Predicate Abstraction • Predicates on program state: lock old = new • States satisfying same predicates are equivalent • Merged into one abstract state • #abstract states is finite

  16. pc lock old new q  3   5  5  0x133a pc lock old new q  4   5  6  0x133a Abstract States and Transitions State 3: unlock(); new++; 4:} … Theorem Prover lock old=new : lock : old=new

  17. pc lock old new q  3   5  5  0x133a pc lock old new q  4   5  6  0x133a Abstraction State 3: unlock(); new++; 4:} … Theorem Prover lock old=new : lock : old=new Existential Lifting

  18. pc lock old new q  3   5  5  0x133a pc lock old new q  4   5  6  0x133a Abstraction State 3: unlock(); new++; 4:} … lock old=new : lock : old=new

  19. Analyze Abstraction Analyze finite graph Over Approximate: Safe ) System Safe No false negatives Problem Spurious counterexamples

  20. Idea 2: Counterex.-Guided Refinement Solution Use spurious counterexamples to refine abstraction!

  21. Idea 2: Counterex.-Guided Refinement Solution Use spurious counterexamples to refine abstraction 1. Add predicates to distinguish states across cut 2. Build refined abstraction Imprecision due to merge

  22. Iterative Abstraction-Refinement Solution Use spurious counterexamples to refine abstraction 1. Add predicates to distinguish states across cut 2. Build refined abstraction -eliminates counterexample 3. Repeat search Till real counterexample or system proved safe [Kurshan et al 93] [Clarke et al 00] [Ball-Rajamani 01]

  23. Lazy Abstraction Yes BLAST Safe Abstract CProgram Refine No Property Trace

  24. Lazy Abstraction Yes BLAST Safe CProgram Instrumented C file With ERROR label spec.opt Property No Trace

  25. Problem: Abstraction is Expensive Reachable Problem #abstract states = 2#predicates Exponential Thm. Prover queries Observe Fraction of state space reachable #Preds ~ 100’s, #States ~ 2100 , #Reach ~ 1000’s

  26. Solution1: Only Abstract Reachable States Safe Solution Build abstraction during search Problem #abstract states = 2#predicates Exponential Thm. Prover queries

  27. Solution2: Don’t Refine Error-Free Regions Error Free Solution Don’t refine error-free regions Problem #abstract states = 2#predicates Exponential Thm. Prover queries

  28. Key Idea: Reachability Tree Initial Unroll Abstraction 1. Pick tree-node (=abs. state) 2. Add children (=abs. successors) 3. On re-visiting abs. state, cut-off 1 2 3 Find min infeasible suffix - Learn new predicates - Rebuild subtree with new preds. 5 4 3

  29. Key Idea: Reachability Tree Initial Unroll Abstraction 1. Pick tree-node (=abs. state) 2. Add children (=abs. successors) 3. On re-visiting abs. state, cut-off 1 2 3 6 Find min infeasible suffix - Learn new predicates - Rebuild subtree with new preds. 4 7 5 3 3 Error Free

  30. Key Idea: Reachability Tree Initial Unroll 1. Pick tree-node (=abs. state) 2. Add children (=abs. successors) 3. On re-visiting abs. state, cut-off 1 2 3 6 Find min spurious suffix - Learn new predicates - Rebuild subtree with new preds. 4 7 8 5 8 3 1 1 3 Error Free S1: Only Abstract Reachable States S2: Don’t refine error-free regions SAFE

  31. Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 1 Reachability Tree Predicates:LOCK

  32. Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK lock() old = new q=q->next 2 LOCK 1 2 Reachability Tree Predicates:LOCK

  33. Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK [q!=NULL] 3 LOCK 1 2 3 Reachability Tree Predicates:LOCK

  34. Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK 3 LOCK q->data = new unlock() new++ 4 : LOCK 4 1 2 3 Reachability Tree Predicates:LOCK

  35. Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK 3 LOCK 4 : LOCK [new==old] 5 : LOCK 5 4 1 2 3 Reachability Tree Predicates:LOCK

  36. Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK 3 LOCK 4 : LOCK 5 : LOCK 5 unlock() 4 : LOCK 1 2 3 Reachability Tree Predicates:LOCK

  37. Analyze Counterexample Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK lock() old = new q=q->next 2 LOCK [q!=NULL] 3 LOCK q->data = new unlock() new++ 4 : LOCK [new==old] 5 : LOCK 5 unlock() 4 : LOCK 1 2 3 Reachability Tree Predicates:LOCK

  38. Analyze Counterexample Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK old = new 2 LOCK 3 LOCK new++ 4 : LOCK [new==old] 5 : LOCK 5 Inconsistent 4 : LOCK new == old 1 2 3 Reachability Tree Predicates:LOCK

  39. Repeat Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 1 Reachability Tree Predicates:LOCK, new==old

  40. Repeat Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK lock() old = new q=q->next 2 LOCK , new==old 1 2 Reachability Tree Predicates:LOCK, new==old

  41. Repeat Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK , new==old 3 LOCK , new==old q->data = new unlock() new++ 4 : LOCK , : new = old 4 1 2 3 Reachability Tree Predicates:LOCK, new==old

  42. Repeat Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK , new==old 3 LOCK , new==old 4 : LOCK , : new = old [new==old] 4 1 2 3 Reachability Tree Predicates:LOCK, new==old

  43. Repeat Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK , new==old 3 LOCK , new==old 4 : LOCK , : new = old [new!=old] 1 : LOCK, : new == old 4 4 1 2 3 Reachability Tree Predicates:LOCK, new==old

  44. Repeat Build-and-Search Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK , new==old SAFE 3 LOCK , new==old 4 4 LOCK , new=old : LOCK , : new = old 1 5 5 : LOCK, : new == old 4 4 4 1 : LOCK , new==old 2 3 Reachability Tree Predicates:LOCK, new==old

  45. Key Idea: Reachability Tree Initial Unroll 1. Pick tree-node (=abs. state) 2. Add children (=abs. successors) 3. On re-visiting abs. state, cut-off 1 2 3 6 Find min spurious suffix - Learn new predicates - Rebuild subtree with new preds. 4 7 8 5 8 3 1 1 3 Error Free S1: Only Abstract Reachable States S2: Don’t refine error-free regions SAFE

  46. Lazy Abstraction Yes Safe Abstract CProgram Refine No Property Trace Problem:Abstraction is Expensive Solution:1.Abstract reachable states, 2. Avoid refining error-free regions Key Idea: Reachability Tree

  47. Plan • Motivation • Lazy Abstraction • Demo • Technical Details

  48. Demo

  49. Plan • Motivation • Lazy Abstraction • Demo • Technical Details

  50. Technical Details Example ( ) { 1: do{ lock(); old = new; q = q->next; 2: if (q != NULL){ 3: q->data = new; unlock(); new ++; } 4:}while(new != old); 5: unlock (); } 1 : LOCK 2 LOCK , new==old SAFE 3 LOCK , new==old 4 4 LOCK , new=old : LOCK , : new = old 1 5 5 : LOCK, : new == old 4 4 4 1 : LOCK , new==old 2 3 Reachability Tree Predicates:LOCK, new==old