Dynamic Symbolic Execution CS 8803 FPL Oct 31, 2012 (Slides adapted from Koushik Sen) 1

2 Today, QA is mostly testing “50% of my company employees are testers, and the rest spends 50% of their time testing!” Bill Gates 1995

3 Software Reliability Importance Software is pervading every aspects of life  Software everywhere Software failures were estimated to cost the US economy about $60 billion annually [NIST 2002]  Improvements in software testing infrastructure may save one- third of this cost Testing accounts for an estimated 50%-80% of the cost of software development [Beizer 1990]

4 Big Picture Safe Programming Languages and Type systems Static Program Analysis Dynamic Program Analysis Model Based Software Development and Analysis Model Checking and Theorem Proving Runtime Monitoring Testing

5 Big Picture Safe Programming Languages and Type systems Model Checking and Theorem Proving Runtime Monitoring Model Based Software Development and Analysis Static Program Analysis Dynamic Program Analysis Testing

6 A Familiar Program: QuickSort void quicksort (int[] a, int lo, int hi) { int i=lo, j=hi, h; int x=a[(lo+hi)/2]; // partition do { while (a[i]<x) i++; while (a[j]>x) j--; if (i<=j) { h=a[i]; a[i]=a[j]; a[j]=h; i++; j--; } } while (i<=j); // recursion if (lo<j) quicksort(a, lo, j); if (i<hi) quicksort(a, i, hi); }

7 A Familiar Program: QuickSort void quicksort (int[] a, int lo, int hi) { int i=lo, j=hi, h; int x=a[(lo+hi)/2]; // partition do { while (a[i]<x) i++; while (a[j]>x) j--; if (i<=j) { h=a[i]; a[i]=a[j]; a[j]=h; i++; j--; } } while (i<=j); // recursion if (lo<j) quicksort(a, lo, j); if (i<hi) quicksort(a, i, hi); } Test QuickSort  Create an array  Initialize the elements of the array  Execute the program on this array How much confidence do I have in this testing method? Is my test suite *Complete*? Can someone generate a small and *Complete* test suite for me?

8 Automated Test Generation Studied since 70’s  King 76, Myers years have passed, and yet no effective solution What Happened?

9 Automated Test Generation Studied since 70’s  King 76, Myers years have passed, and yet no effective solution What Happened?  Program-analysis techniques were expensive  Automated theorem proving and constraint solving techniques were not efficient

10 Automated Test Generation Studied since 70’s  King 76, Myers years have passed, and yet no effective solution What Happened?  Program-analysis techniques were expensive  Automated theorem proving and constraint solving techniques were not efficient Recent years have seen remarkable strides in static analysis and constraint solving  SLAM, BLAST, ESP, Bandera, Saturn, MAGIC

11 Automated Test Generation Studied since 70’s  King 76, Myers years have passed, and yet no effective solution What Happened?  Program analysis techniques were expensive  Automated theorem proving and constraint solving techniques were not efficient Recent years have seen remarkable strides in static analysis and constraint solving  SLAM, BLAST, ESP, Bandera, Saturn, MAGIC Question: Can we use similar techniques in Automated Testing?

12 Systematic Automated Testing Testing Static Analysis Automated Theorem Proving Model-Checking and Formal Methods Constraint Solving

13 CUTE and DART Combine random testing (concrete execution) and symbolic testing (symbolic execution) [PLDI’05, FSE’05, FASE’06, CAV’06,ISSTA’07, ICSE’07] Concrete + Symbolic = Concolic

14 Goal Automated Unit Testing of real-world C and Java Programs  Generate test inputs  Execute unit under test on generated test inputs so that all reachable statements are executed  Any assertion violation gets caught

15 Goal Automated Unit Testing of real-world C and Java Programs  Generate test inputs  Execute unit under test on generated test inputs so that all reachable statements are executed  Any assertion violation gets caught Our Approach:  Explore all execution paths of an Unit for all possible inputs Exploring all execution paths ensure that all reachable statements are executed

16 Execution Paths of a Program Can be seen as a binary tree with possibly infinite depth  Computation tree Each node represents the execution of a “if then else” statement Each edge represents the execution of a sequence of non-conditional statements Each path in the tree represents an equivalence class of inputs

17 Example of Computation Tree void test_me(int x, int y) { if(2*x==y){ if(x != y+10){ printf(“I am fine here”); } else { printf(“I should not reach here”); ERROR; } 2*x==y x!=y+10 NY NY ERROR

18 Concolic Testing: Finding Security and Safety Bugs Divide by 0 Error x = 3 / i; Buffer Overflow a[i] = 4;

19 Concolic Testing: Finding Security and Safety Bugs Divide by 0 Error if (i !=0) x = 3 / i; else ERROR; Buffer Overflow if (0<=i && i < a.length) a[i] = 4; else ERROR; Key: Add Checks Automatically and Perform Concolic Testing

20 Existing Approach I Random testing  generate random inputs  execute the program on generated inputs Probability of reaching an error can be astronomically less test_me(int x){ if(x==94389){ ERROR; } Probability of hitting ERROR = 1/2 32

21 Existing Approach II Symbolic Execution  use symbolic values for input variables  execute the program symbolically on symbolic input values  collect symbolic path constraints  use theorem prover to check if a branch can be taken Does not scale for large programs test_me(int x) { if ((x%10)*4!=17) { ERROR; } else { ERROR; } Symbolic execution will say both branches are reachable: False positive

22 Existing Approach II Symbolic Execution  use symbolic values for input variables  execute the program symbolically on symbolic input values  collect symbolic path constraints  use theorem prover to check if a branch can be taken Does not scale for large programs test_me(int x) { if (bbox(x)!=17) { ERROR; } else { ERROR; } Symbolic execution will say both branches are reachable: False positive

23 Concolic Testing Approach Random Test Driver:  random values for x and y Probability of reaching ERROR is extremely low int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; }

24 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7x = x 0, y = y 0

25 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7, z = 14 x = x 0, y = y 0, z = 2*y 0

26 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7, z = 14 x = x 0, y = y 0, z = 2*y 0 2*y 0 != x 0

27 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition 2*y 0 != x 0 Solve: 2*y 0 == x 0 Solution: x 0 = 2, y 0 = 1 x = 22, y = 7, z = 14 x = x 0, y = y 0, z = 2*y 0

28 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 2, y = 1x = x 0, y = y 0

29 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 2, y = 1, z = 2 x = x 0, y = y 0, z = 2*y 0

30 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 2, y = 1, z = 2 x = x 0, y = y 0, z = 2*y 0 2*y 0 == x 0

31 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 2, y = 1, z = 2 x = x 0, y = y 0, z = 2*y 0 2*y 0 == x 0 x 0 <= y 0 +10

32 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 2, y = 1, z = 2 x = x 0, y = y 0, z = 2*y 0 Solve: (2*y 0 == x 0 ) and (x 0 > y ) Solution: x 0 = 30, y 0 = 15 2*y 0 == x 0 x 0 <= y 0 +10

33 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 30, y = 15x = x 0, y = y 0

34 Concolic Testing Approach int double (int v) { return 2*v; } void testme (int x, int y) { z = double (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 30, y = 15x = x 0, y = y 0 2*y 0 == x 0 x 0 > y Program Error

35 Explicit Path (not State) Model Checking Traverse all execution paths one by one to detect errors  assertion violations  program crash  uncaught exceptions combine with valgrind to discover memory errors F T FF F F T T T T T T

36 Explicit Path (not State) Model Checking Traverse all execution paths one by one to detect errors  assertion violations  program crash  uncaught exceptions combine with valgrind to discover memory errors F T FF F F T T T T T T

37 Explicit Path (not State) Model Checking Traverse all execution paths one by one to detect errors  assertion violations  program crash  uncaught exceptions combine with valgrind to discover memory errors F T FF F F T T T T T T

38 Explicit Path (not State) Model Checking Traverse all execution paths one by one to detect errors  assertion violations  program crash  uncaught exceptions combine with valgrind to discover memory errors F T FF F F T T T T T T

39 Explicit Path (not State) Model Checking Traverse all execution paths one by one to detect errors  assertion violations  program crash  uncaught exceptions combine with valgrind to discover memory errors F T FF F F T T T T T T

40 Explicit Path (not State) Model Checking Traverse all execution paths one by one to detect errors  assertion violations  program crash  uncaught exceptions combine with valgrind to discover memory errors F T FF F F T T T T T T

41 Novelty: Simultaneous Concrete and Symbolic Execution int foo (int v) { return (v*v) % 50; } void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7x = x 0, y = y 0

42 int foo (int v) { return (v*v) % 50; } void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7, z = 49 x = x 0, y = y 0, z = (y 0 *y 0 )%50 (y 0 *y 0 )%50 !=x 0 Solve: (y 0 *y 0 )%50 == x 0 Don’t know how to solve! Stuck? Novelty: Simultaneous Concrete and Symbolic Execution

43 void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7, z = 49 x = x 0, y = y 0, z = foo (y 0 ) foo (y 0 ) !=x 0 Novelty: Simultaneous Concrete and Symbolic Execution Solve: foo (y 0 ) == x 0 Don’t know how to solve! Stuck?

44 int foo (int v) { return (v*v) % 50; } void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7, z = 49 x = x 0, y = y 0, z = (y 0 *y 0 )%50 (y 0 *y 0 )%50 !=x 0 Solve: (y 0 *y 0 )%50 == x 0 Don’t know how to solve! Not Stuck! Use concrete state Replace y 0 by 7 (sound) Novelty: Simultaneous Concrete and Symbolic Execution

45 int foo (int v) { return (v*v) % 50; } void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 22, y = 7, z = 48 x = x 0, y = y 0, z = !=x 0 Solve: 49 == x 0 Solution : x 0 = 49, y 0 = 7 Novelty: Simultaneous Concrete and Symbolic Execution

46 int foo (int v) { return (v*v) % 50; } void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 49, y = 7x = x 0, y = y 0 Novelty: Simultaneous Concrete and Symbolic Execution

47 int foo (int v) { return (v*v) % 50; } void testme (int x, int y) { z = foo (y); if (z == x) { if (x > y+10) { ERROR; } Concrete Execution Symbolic Execution concrete state symbolic state path condition x = 49, y = 7, z = 49 x = x 0, y = y 0, z = 49 2*y 0 == x 0 x 0 > y Program Error Novelty: Simultaneous Concrete and Symbolic Execution

48 Concolic Testing: A Middle Approach + Complex programs + Efficient - Less coverage + No false positive - Simple programs - Not efficient + High coverage - False positive Random Testing Symbolic Testing Concolic Testing + Complex programs +/- Somewhat efficient + High coverage + No false positive

49 Implementations DART and CUTE for C programs jCUTE for Java programs  Goto for CUTE and jCUTE binarieshttp://srl.cs.berkeley.edu/~ksen/ MSR has four implementations  SAGE, PEX, YOGI, Vigilante Similar tool: EXE at Stanford Easiest way to use and to develop on top of CUTE  Implement concolic testing yourself

50 Another Example: Testing Data Structures typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Random Test Driver: random memory graph reachable from p random value for x Probability of reaching abort( ) is extremely low

51 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0 p, x=236 NULL

52 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0 p, x=236 NULL

53 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p=p 0, x=x 0 p, x=236 NULL

54 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p=p 0, x=x 0 p, x=236 NULL !(p 0 !=NULL )

55 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p=p 0, x=x 0 p, x=236 NULL p 0 =NULL solve: x 0 >0 and p 0  NULL

56 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p=p 0, x=x 0 p, x=236 NULL p 0 =NULL solve: x 0 >0 and p 0  NULL x 0 =236, p NULL

57 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634

58 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634 x 0 >0

59 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634 x 0 >0 p 0  NULL

60 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634 x 0 >0 p 0  NULL 2x 0 +1  v 0

61 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634 x 0 >0 p 0  NULL 2x 0 +1  v 0

62 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634 x 0 >0 p 0  NULL 2x 0 +1  v 0 solve: x 0 >0 and p 0  NULL and 2x 0 +1=v 0

63 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=236 NULL 634 x 0 >0 p 0  NULL 2x 0 +1  v 0 solve: x 0 >0 and p 0  NULL and 2x 0 +1=v 0 x 0 =1, p 0 3 NULL

64 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3

65 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0

66 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0 p 0  NULL

67 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0 p 0  NULL 2x 0 +1=v 0

68 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0 p 0  NULL 2x 0 +1=v 0 n0p0n0p0

69 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0 p 0  NULL 2x 0 +1=v 0 n0p0n0p0

70 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints solve: x 0 >0 and p 0  NULL and 2x 0 +1=v 0 and n 0 =p 0 p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0 p 0  NULL 2x 0 +1=v 0 n0p0n0p0

71 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints solve: x 0 >0 and p 0  NULL and 2x 0 +1=v 0 and n 0 =p 0 x 0 =1, p 0 3 p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 NULL 3 x 0 >0 p 0  NULL 2x 0 +1=v 0 n0p0n0p0

72 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 3

73 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 3

74 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p 0  NULL p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 3

75 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p 0  NULL 2x 0 +1=v 0 p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 3

76 CUTE Approach typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; } Concrete Execution Symbolic Execution concrete state symbolic state constraints x 0 >0 p 0  NULL 2x 0 +1=v 0 n0=p0n0=p0 p=p 0, x=x 0, p->v=v 0, p->next=n 0 p, x=1 3 Program Error

77 Pointer Inputs: Input Graph typedef struct cell { int v; struct cell *next; } cell; int f(int v) { return 2*v + 1; } int testme(cell *p, int x) { if (x > 0) if (p != NULL) if (f(x) == p->v) if (p->next == p) abort(); return 0; }

78 CUTE in a Nutshell Generate concrete inputs one by one  each input leads program along a different path

79 CUTE in a Nutshell Generate concrete inputs one by one  each input leads program along a different path On each input execute program both concretely and symbolically

80 CUTE in a Nutshell Generate concrete inputs one by one  each input leads program along a different path On each input execute program both concretely and symbolically  Both cooperate with each other concrete execution guides the symbolic execution

81 CUTE in a Nutshell Generate concrete inputs one by one  each input leads program along a different path On each input execute program both concretely and symbolically  Both cooperate with each other concrete execution guides the symbolic execution concrete execution enables symbolic execution to overcome incompleteness of theorem prover  replace symbolic expressions by concrete values if symbolic expressions become complex  resolve aliases for pointer using concrete values  handle arrays naturally

82 CUTE in a Nutshell Generate concrete inputs one by one  each input leads program along a different path On each input execute program both concretely and symbolically  Both cooperate with each other concrete execution guides the symbolic execution concrete execution enables symbolic execution to overcome incompleteness of theorem prover  replace symbolic expressions by concrete values if symbolic expressions become complex  resolve aliases for pointer using concrete values  handle arrays naturally symbolic execution helps to generate concrete input for next execution  increases coverage

83 Instrumentation

84 Instrumented Program Maintains a symbolic state  maps each memory location used by the program to symbolic expressions over symbolic input variables Maintains a path constraint  a sequence of constraints C 1, C 2,…, C k such that C i s are symbolic constraints over symbolic input variables C 1 ∧ C 2 ∧ … ∧ C k holds over the path currently executed by the program

85 Instrumented Program Maintains a symbolic state  maps each memory location used by the program to symbolic expressions over symbolic input variables Maintains a path constraint  a sequence of constraints C 1, C 2,…, C k such that C i s are symbolic constraints over symbolic input variables C 1 ∧ C 2 ∧ … ∧ C k holds over the path currently executed by the program Arithmetic Expressions a 1 x 1 +…+a n x n +c Pointer Expressions x

86 Instrumented Program Maintains a symbolic state  maps each memory location used by the program to symbolic expressions over symbolic input variables Maintains a path constraint  a sequence of constraints C 1, C 2,…, C k such that C i s are symbolic constraints over symbolic input variables C 1 ∧ C 2 ∧ … ∧ C k holds over the path currently executed by the program Arithmetic Expressions a 1 x 1 +…+a n x n +c Pointer Expressions x Arithmetic Constraints a 1 x 1 +…+a n x n ¸ 0 Pointer Constraints x=y x  y x=NULL x  NULL

87 Constraint Solving Path constraint C 1 ∧ C 2 ∧ … ∧ C k ∧ … ∧ C n

88 Constraint Solving Path constraint C 1 ∧ C 2 ∧ … ∧ C k ∧ … ∧ C n Solve C 1 ∧ C 2 ∧ … ∧ !C k to generate next input

89 Constraint Solving Path constraint C 1 ∧ C 2 ∧ … ∧ C k ∧ … ∧ C n Solve C 1 ∧ C 2 ∧ … ∧ !C k to generate next input If C k is pointer constraint then invoke pointer solver C i1 ∧ C i2 ∧ … ∧ !C k where ij in [1..k-1] and C ij is pointer constraint If C k is arithmetic constraint then invoke linear solver C i1 ∧ C i2 ∧ … ∧ !C k where ij in [1..k-1] and C ij is arithmetic constraint

90 SGLIB: popular library for C data-structures Used in Xrefactory a commercial tool for refactoring C/C++ programs Found two bugs in sglib  reported them to authors  fixed in sglib Bug 1:  doubly-linked list library segmentation fault occurs when a non-zero length list is concatenated with a zero-length list discovered in 140 iterations ( < 1second) Bug 2:  hash-table an infinite loop in hash table is member function 193 iterations (1 second)

91 SGLIB: popular library for C data-structures Name Run time in seconds # of Iterations # of Branches Explored % Branch Coverage # of Functions Tested # of Bugs Found Array Quick Sort Array Heap Sort Linked List Sorted List Doubly Linked List Hash Table Red Black Tree 26291,000,

92 Experiments: Needham-Schroeder Protocol Tested a C implementation of a security protocol (Needham-Schroeder) with a known attack  600 lines of code  Took less than 13 seconds on a machine with 1.8GHz Xeon processor and 2 GB RAM to discover middle-man attack In contrast, a software model-checker (VeriSoft) took 8 hours

93 Testing Data-structures of CUTE itself Unit tested several non-standard data- structures implemented for the CUTE tool  cu_depend (used to determine dependency during constraint solving using graph algorithm)  cu_linear (linear symbolic expressions)  cu_pointer (pointer symbolic expresiions) Discovered a few memory leaks and a copule of segmentation faults  these errors did not show up in other uses of CUTE  for memory leaks we used CUTE in conjunction with Valgrind