ASPLOS'18: Sulong, and Thanks For All the Bugs: Finding Errors in C Programs by Abstracting from the Native Execution Model

Talk at the 23rd ACM International Conference on Architectural Support for Programming Languages and Operating Systems (https://www.asplos2018.org/)

Transcript

1. Sulong, and Thanks For All the Bugs Finding Errors in C Programs by Abstracting from the Native Execution Model Manuel Rigger1, Roland Schatz2, René Mayrhofer1, Matthias Grimmer2, Hanspeter Mössenböck1 1 Johannes Kepler University Linz, Austria 2 Oracle Labs, Austria ASPLOS ’18, March 27, 2018, Williamsburg, VA, USA
2. Claim: Unsafe Languages can be Executed Safely and Efficiently on the Java Virtual Machine 2
3. Claim: Unsafe Languages can be Executed Safely and Efficiently on the Java Virtual Machine 3
4. What are Unsafe Languages? 4 Unsafe Languages Do not specify an operation for all inputs e.g., C Safe Languages Strictly define all operations e.g., Java (Felleisen et al. 1999)
5. Buffer Overflows 5 int *arr = malloc(3 * sizeof(int)); arr[5] = …
6. Buffer Overflows 5 int *arr = malloc(3 * sizeof(int)); arr[5] = … C Undefined Behavior
7. Buffer Overflows 5 int *arr = malloc(3 * sizeof(int)); arr[5] = … Java C Undefined Behavior ArrayIndexOutOfBoundsException int[] arr = new int[3]; arr[5] = …
8. Use-after-free Errors 6 free(arr); arr[0] = …
9. Use-after-free Errors 6 free(arr); arr[0] = … C Undefined Behavior
10. Use-after-free Errors 6 free(arr); arr[0] = … C Undefined Behavior NullPointerException Java arr = null; arr[0] =
11. Idea 7 Map the semantics of a C Program to Java to automatically detect memory safety errors
12. State of the Art 8 a.out Clang/GCC C ./a.out Hello world!
13. State of the Art Compile-time instrumentation • AddressSanitizer (ASan) (Serebryany et al. 2012) • SoftBound+CETS (Nagarakatte et al. 2009, 2010) 8 a.out Clang/GCC C ./a.out Hello world!
14. State of the Art Compile-time instrumentation • AddressSanitizer (ASan) (Serebryany et al. 2012) • SoftBound+CETS (Nagarakatte et al. 2009, 2010) 8 a.out Clang/GCC C ./a.out Hello world! Run-time instrumentation • Valgrind (Nethercote et al. 2007) • Dr. Memory (Bruening et al. 2011)
15. State of the Art 9 a.out Clang/GCC C ./a.out Hello world! Such tools were very helpful in finding bugs in widely used code
16. Can we do better? 10 a.out Clang/GCC C ./a.out Hello world! Static compilers: optimize code based on Undefined Behavior Bug-finding tools: find bugs assuming that violations are visible side effects (Wang et al. 2012, D'Silva 2015)
17. Can we do better? 10 a.out Clang/GCC C ./a.out Hello world! Static compilers: optimize code based on Undefined Behavior Bug-finding tools: find bugs assuming that violations are visible side effects (Wang et al. 2012, D'Silva 2015)
18. Can we do better? 10 a.out Clang/GCC C ./a.out Hello world! Static compilers: optimize code based on Undefined Behavior Bug-finding tools: find bugs assuming that violations are visible side effects struct sock *sk = tun->sk; if (!tun) return POLLERR; (Wang et al. 2012, D'Silva 2015)
19. Can we do better? 10 a.out Clang/GCC C ./a.out Hello world! Static compilers: optimize code based on Undefined Behavior Bug-finding tools: find bugs assuming that violations are visible side effects struct sock *sk = tun->sk; if (!tun) return POLLERR; (Wang et al. 2012, D'Silva 2015)
20. Can we do better? 11 a.out Clang/GCC C ./a.out Hello world! Current approaches do not abstract from the underlying machine/native execution model
21. Can we do better? 11 a.out Clang/GCC C ./a.out Hello world! Current approaches do not abstract from the underlying machine/native execution model Manually adding instrumentation is error-prone
22. Claim: Unsafe Languages can be Executed Safely and Efficiently on the Java Virtual Machine 12
23. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0
24. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0
25. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM We are currently using a custom libc implementation (without system calls) -O0
26. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM (Lattner 2004) -O0
27. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM (Lattner 2004) Executing LLVM IR allows us to also execute other unsafe languages -O0
28. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0
29. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0
30. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0 Unaware of the underlying machine, execution model, and ABI
31. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM (Würthinger et al. 2013) -O0
32. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM (Würthinger et al. 2013) -O0 Truffle and Graal allow Safe Sulong to reach “native speeds”
33. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0
34. System Overview 13 LLVM IR Interpreter LLVM IR Clang program.c libc.c Truffle Graal JVM -O0 All checks are automatically performed by the underlying JVM
35. Prevent Out-Of-Bounds Accesses 14 int *arr = malloc(3 * sizeof(int)) arr[5] = … ManagedAddress offset=5 data I32Array contents {0, 0, 0}
36. Prevent Out-Of-Bounds Accesses contents[5]  ArrayIndexOutOfBoundsException 14 int *arr = malloc(3 * sizeof(int)) arr[5] = … ManagedAddress offset=5 data I32Array contents {0, 0, 0}
37. ManagedAddress offset=0 data I32Array contents=null Prevent Use-After-Free Errors 15 free(arr); arr[0] = …
38. ManagedAddress offset=0 data I32Array contents=null Prevent Use-After-Free Errors 15 free(arr); arr[0] = …
39. ManagedAddress offset=0 data I32Array contents=null Prevent Use-After-Free Errors contents[0] NullPointerException 15 free(arr); arr[0] = …
40. ManagedAddress offset=0 data I32Array contents=null Prevent Use-After-Free Errors contents[0] NullPointerException 15 free(arr); arr[0] = … Safe Sulong can detect other categories of errors (e.g., double-free errors)
41. Evaluation • Found 68 errors in small open-source projects • Safe Sulong found 8 errors that were both not found by ASan and Valgrind • Compiler optimizations (ASan –O3) prevented the detection of 4 additional bugs • Valgrind detected half of the errors 16
42. Evaluation: Example ASan 17 int main(int argc, char** argv) { printf("%d %s\n", argc, argv[100]); } ASan does not instrument the main() arguments since they are allocated by libc https://github.com/google/sanitizers/issues/762
43. Claim: Unsafe Languages can be Executed Safely and Efficiently on the Java Virtual Machine 18
44. Example Program 19 void processRequests () { int i = 0; do { processPacket (); i ++; } while (i < 10000) ; } C
45. Example Program 19 void processRequests () { int i = 0; do { processPacket (); i ++; } while (i < 10000) ; } define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR Clang C
46. 20 define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR Implementation of Operations
47. 20 define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR Executable Abstract Syntax Tree Implementation of Operations write %2 add read %i 1
48. 21 define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR Implementation of Basic Blocks
49. 21 define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR Executable Abstract Syntax Tree Implementation of Basic Blocks Block1
50. Implementation of Control Flow Support 22 define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR
51. Implementation of Control Flow Support 22 define void @processRequests () #0 { ; ( basic block 0) br label %1 ; <label >:1 ( basic block 1) %i = phi i32 [ 0, %0 ], [ %2 , %1 ] call void @processPacket () %2 = add nsw i32 %i, 1 %3 = icmp slt i32 %2 , 10000 br i1 %3 , label %1 , label %4 ; <label >:4 ( basic block 2) ret void } LLVM IR Block0 Block1 Block2 Basic Block Dispatch Node 1 2 -1 1
52. Compilation • For frequently executed functions • Partial evaluation: inline execute methods of the graph (recursively) • Further optimize the graph 23 Block0 Block1 Block2 Basic Block Dispatch Node 1 2 -1 1
53. Block0 Block1 Block2 Basic Block Dispatch Node 1 2 -1 1 Compiler 24 int blockIndex = 0; block0: blockIndex = 1 %i.0 = 0 block1: while (true): processPacket() %2 = %i.0 + 1 %3 = %2 < 10000 if %3: blockIndex = 1 %i.0 = %2 continue; else: blockIndex = 2 block2: blockIndex = -1 return Unrolling of the interpreter loop
54. Block0 Block1 Block2 Basic Block Dispatch Node 1 2 -1 1 Compiler 24 int blockIndex = 0; block0: blockIndex = 1 %i.0 = 0 block1: while (true): processPacket() %2 = %i.0 + 1 %3 = %2 < 10000 if %3: blockIndex = 1 %i.0 = %2 continue; else: blockIndex = 2 block2: blockIndex = -1 return Unrolling of the interpreter loop Graal further optimizes the partially evaluated interpreter
55. Safe Semantics • Safe by design: errors result in exceptions • Invalid memory accesses are not optimized away 25
56. Evaluation: Peak Performance 26 lower is better
57. Evaluation: Peak Performance 27 lower is better
58. Evaluation: Peak Performance 27 Small benchmarks since Safe Sulong failed executing SPEC  preliminary results lower is better
59. Evaluation: Peak Performance 28 lower is better
60. Evaluation: Peak Performance 28 Baseline is Clang –O0, Safe Sulong is faster in all but one case lower is better
61. Evaluation: Peak Performance 29 lower is better
62. Evaluation: Peak Performance 29 Safe Sulong is close to Clang –O3 in some cases lower is better
63. Evaluation: Peak Performance 30 lower is better
64. Evaluation: Peak Performance 30 Safe Sulong –O0 is mostly faster than ASan –O0 lower is better
65. Future Work and Summary 31
66. 32 Executing libc and Other System Libraries
67. 32 asm("rdtsc":"=a"(tickl),"=d"(tickh)); Inline assembly Executing libc and Other System Libraries (Rigger et al. 2018)
68. 32 if (__builtin_expect(x, 0)) foo (); asm("rdtsc":"=a"(tickl),"=d"(tickh)); Inline assembly Executing libc and Other System Libraries Compiler builtins (Rigger et al. 2018)
69. 32 if (__builtin_expect(x, 0)) foo (); asm("rdtsc":"=a"(tickl),"=d"(tickh)); Inline assembly Executing libc and Other System Libraries Compiler builtins getcwd(buf, size); System calls (Rigger et al. 2018)
70. 32 if (__builtin_expect(x, 0)) foo (); asm("rdtsc":"=a"(tickl),"=d"(tickh)); Inline assembly Executing libc and Other System Libraries Compiler builtins getcwd(buf, size); System calls Implementing them will allow Safe Sulong to execute existing libcs (and SPEC) (Rigger et al. 2018)
71. Summary 33 @RiggerManuel Approaches are based on “unsafe” compilers Safe Sulong automatically detects errors It reaches good peak performance We are still working on completeness
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