Sanitizer¶

Introduction¶

寫程式常碰到有 bug，用 C 或 C++ 這種程式語言寫的話， bug 又常跟記憶體有關，這時常常會使用 Valgrind 來找問題，而近幾年又多了一些 compiler 參數可以幫忙。

當要跑的平台上可以用 compiler 參數來檢查時，可以考慮就先使用 compiler 參數，如果要用的 compiler 沒支援這參數或是 compiler 沒支援要跑的平台，那麼可以考慮 Valgrind，雖然比較慢，但是可用的平台和能偵測的項目很多。

compiler 的 sanitizer 這邊有些細部要注意，在一些條件下可能會不支援。

Clang
- AddressSanitizer
  
  memory error detector
  
  a compiler instrumentation module and a run-time library
- MemorySanitizer
  
  detector of uninitialized reads
  
  a compiler instrumentation module and a run-time library
- ThreadSanitizer
  
  detects data races
- LeakSanitizer
  
  detects memory leaks
- UndefinedBehaviorSanitier

這三個只能分開使用，不能一起用：

AddressSanitizer
ThreadSanitizer
MemorySanitizer

UndefinedBehaviorSanitier 可以和其他種結合
LeakSanitizer 目前只可以和 AddressSanitizer 一起用 (或自己用)

Name	Slowdown	Memory Overhead	Option
AddressSanitizer	2x	4x	-fsanitize=address
ThreadSanitizer	5x ~ 15x	5x ~ 10x	-fsanitize=thread
MemorySanitizer	3x (4x with origin tracking)	2x (3x with origin tracking)	-fsanitize=memory
LeakSanitizer	0x (with ASan)		-fsanitize=leak
UndefinedBehaviorSanitier	0x		-fsanitize=undefined

+----------------------------+   no
| 你想要找 memory 相關的 bug |---------> 不在這邊的討論範圍內
+----------------------------+
            |
            | yes
            |
            v
+-------------------------+  no
| 專案使用 Clang/GCC 編譯 |---------> 用 Valgrind
+-------------------------+
            |                                          +---------------------+
            | yes                                   +->| 找其他 Memory Error |--+
            |                                       |  +---------------------+  |
            v                                       |                           |
+----------------------+  no   +--------------+  no |  +----------------+       |
| 尋找存取未初始化的值 |------>| 找 data race |-----+->| 找 memory leak |       |
+----------------------+       +--------------+        +----------------+       |
            |                          |                      |                 |
            | yes                      | yes                  | yes             | yes
            |                          |                      |                 |
            v                          v                      v                 v
    MemorySanitizer            ThreadSanitizer           LeakSanitizer    AddressSanitizer
                                                              |                 |
                                                              |                 |
                                                              +--------+--------+
                                                                       |
                                                                       v
                                                        LeakSanitizer + AddressSanitizer

+----------------------+
| 找 undefine behavior |
+----------------------+
            |
            |
            |
            v
UndefinedBehaviorSanitier

(目前提到的 Compiler Instrumentation 對於 JIT 這種 code 還不太適用)

利用這邊的工具除錯時，推薦的優化參數： -O1 -fno-omit-frame-pointer -fno-optimize-sibling-calls
- -O1 是為了關掉 inline
- -fno-omit-frame-pointer 是為了更好的 stack trace 訊息
- -fno-optimize-sibling-calls 是為了關掉 tail call elimination

PASS 1 : -fsanitize=leak -fsanitize=address -fsanitize=undefined
- Memory Leaks
- 大部分的 Memory 相關錯誤
- Undefined Behavior
PASS 2 : -fsanitize=memory
- 找出未初始化的值的使用
PASS 3 : -fsanitize=thread
- 找出 data races

AddressSanitizer¶

AddressSanitizer 目前支援以下幾種情況：

(OOB) Out-of-bounds accesses to heap, stack and globals
(UAF) Use-after-free
(UAR) Use-after-return (to some extent)
Double-free, invalid free
Memory leaks (experimental)

(最後生成 executable 時，需要把 AddressSanitizer run-time library link 上去，所以最後的 link step 要用 clang，不能用 ld)

遇到錯誤會馬上停止，developer 會被強迫修正問題後才能繼續執行。

Example 1¶

Source Code :

int main() {
    // UAF (Use After Free)
    int *array = new int[42];
    delete [] array;
    return array[0];    // BOOM
}

Compile :

$ clang++ -O1 -g -fsanitize=address -fno-omit-frame-pointer example.cpp -o example

Run :

$ ./example
=================================================================
==26771==ERROR: AddressSanitizer: heap-use-after-free on address 0x60f00000ef50 at pc 0x0000004dc22c bp 0x7fffc3c85060 sp 0x7fffc3c85058
READ of size 4 at 0x60f00000ef50 thread T0
    #0 0x4dc22b in main /tmp/example.cpp:5:12
    #1 0x300042078f in __libc_start_main (/usr/lib/libc.so.6+0x300042078f)
    #2 0x434fa8 in _start (/tmp/example+0x434fa8)

0x60f00000ef50 is located 0 bytes inside of 168-byte region [0x60f00000ef50,0x60f00000eff8)
freed by thread T0 here:
    #0 0x4dbb22 in operator delete[](void*) (/tmp/example+0x4dbb22)
    #1 0x4dc1fa in main /tmp/example.cpp:4:5
    #2 0x300042078f in __libc_start_main (/usr/lib/libc.so.6+0x300042078f)

previously allocated by thread T0 here:
    #0 0x4db562 in operator new[](unsigned long) (/tmp/example+0x4db562)
    #1 0x4dc1ef in main /tmp/example.cpp:3:18
    #2 0x300042078f in __libc_start_main (/usr/lib/libc.so.6+0x300042078f)

SUMMARY: AddressSanitizer: heap-use-after-free /tmp/example.cpp:5 main
Shadow bytes around the buggy address:
0x0c1e7fff9d90: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9da0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9db0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9dc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9dd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c1e7fff9de0: fa fa fa fa fa fa fa fa fa fa[fd]fd fd fd fd fd
0x0c1e7fff9df0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fa
0x0c1e7fff9e00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9e10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9e20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff9e30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable:           00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone:       fa
Heap right redzone:      fb
Freed heap region:       fd
Stack left redzone:      f1
Stack mid redzone:       f2
Stack right redzone:     f3
Stack partial redzone:   f4
Stack after return:      f5
Stack use after scope:   f8
Global redzone:          f9
Global init order:       f6
Poisoned by user:        f7
Container overflow:      fc
Array cookie:            ac
Intra object redzone:    bb
ASan internal:           fe
Left alloca redzone:     ca
Right alloca redzone:    cb
==26771==ABORTING

Compile :

$ clang++ -O1 -g -fsanitize=address -fno-omit-frame-pointer example.cpp -o example

Run with Valgrind :

$ valgrind ./example
==28951== Memcheck, a memory error detector
==28951== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==28951== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==28951== Command: ./example
==28951==
==28951== Invalid read of size 4
==28951==    at 0x4005A7: main (in /tmp/example)
==28951==  Address 0xfff000674 is on thread 1's stack
==28951==  412 bytes below stack pointer
==28951==
==28951==
==28951== HEAP SUMMARY:
==28951==     in use at exit: 72,704 bytes in 1 blocks
==28951==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==28951==
==28951== LEAK SUMMARY:
==28951==    definitely lost: 0 bytes in 0 blocks
==28951==    indirectly lost: 0 bytes in 0 blocks
==28951==      possibly lost: 0 bytes in 0 blocks
==28951==    still reachable: 72,704 bytes in 1 blocks
==28951==         suppressed: 0 bytes in 0 blocks
==28951== Rerun with --leak-check=full to see details of leaked memory
==28951==
==28951== For counts of detected and suppressed errors, rerun with: -v
==28951== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

Example 2 (Can Not Detect) (Neither Valgrind ...)¶

Source Code :

int main() {
    int *ptr= nullptr;

    {
        int array[42];
        array[0] = 42;
        ptr = array;
    }

    ptr[0] = 99;

    return ptr[0];    // ptr points to an array which is out of scope !!!
}

Compile :

$ clang++ -O1 -g -fsanitize=address -fno-omit-frame-pointer example.cpp -o example

Run :

$ ./example
# nothing happen ...

Example 3 (Can Not Detect) (Valgrind can find it !!!)¶

Source Code :

void f(int **pptr) {
    int array[42];
    array[0] = 42;
    *pptr = array;
}

int main() {
    int *ptr= nullptr;
    f(&ptr);
    ptr[0] = 99;
    return ptr[0];    // ptr points to an array which is out of scope !!!
}

Compile :

$ clang++ -O1 -g -fsanitize=address -fno-omit-frame-pointer example.cpp -o example

Run :

$ ./example
# nothing happen ...

Compile :

$ clang++ -O1 -g -fsanitize=address -fno-omit-frame-pointer example.cpp -o example

Run with Valgrind :

$ valgrind ./example
==13109== Memcheck, a memory error detector
==13109== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==13109== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==13109== Command: ./example
==13109==
==13109== Invalid write of size 4
==13109==    at 0x4005AD: main (example.cpp:10)
==13109==  Address 0xfff000760 is on thread 1's stack
==13109==  176 bytes below stack pointer
==13109==
==13109== Invalid read of size 4
==13109==    at 0x4005B7: main (in /tmp/example)
==13109==  Address 0xfff000760 is on thread 1's stack
==13109==  176 bytes below stack pointer
==13109==
==13109==
==13109== HEAP SUMMARY:
==13109==     in use at exit: 72,704 bytes in 1 blocks
==13109==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==13109==
==13109== LEAK SUMMARY:
==13109==    definitely lost: 0 bytes in 0 blocks
==13109==    indirectly lost: 0 bytes in 0 blocks
==13109==      possibly lost: 0 bytes in 0 blocks
==13109==    still reachable: 72,704 bytes in 1 blocks
==13109==         suppressed: 0 bytes in 0 blocks
==13109== Rerun with --leak-check=full to see details of leaked memory
==13109==
==13109== For counts of detected and suppressed errors, rerun with: -v
==13109== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

Example 4 (Can Not Detect) (Valgrind can find it !!!)¶

from address-sanitizer - Example: UseAfterReturn

Source Code :

int *ptr;
__attribute__((noinline))
void FunctionThatEscapesLocalObject() {
    int local[100];
    ptr = &local[0];
}

int main(int argc, char **argv) {
    FunctionThatEscapesLocalObject();
    return ptr[argc];
}

Compile :

$ clang++ -O1 -g -fsanitize=address -fno-omit-frame-pointer example.cpp -o example

Run :

$ ./example
# nothing happen ...

Compile :

$ clang++ -O1 -g -fno-omit-frame-pointer example.cpp -o example

Run with Valgrind :

$ valgrind ./example
==27388== Memcheck, a memory error detector
==27388== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==27388== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==27388== Command: ./example
==27388==
==27388== Invalid read of size 4
==27388==    at 0x4005A7: main (in /tmp/example)
==27388==  Address 0xfff000674 is on thread 1's stack
==27388==  412 bytes below stack pointer
==27388==
==27388==
==27388== HEAP SUMMARY:
==27388==     in use at exit: 72,704 bytes in 1 blocks
==27388==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==27388==
==27388== LEAK SUMMARY:
==27388==    definitely lost: 0 bytes in 0 blocks
==27388==    indirectly lost: 0 bytes in 0 blocks
==27388==      possibly lost: 0 bytes in 0 blocks
==27388==    still reachable: 72,704 bytes in 1 blocks
==27388==         suppressed: 0 bytes in 0 blocks
==27388== Rerun with --leak-check=full to see details of leaked memory
==27388==
==27388== For counts of detected and suppressed errors, rerun with: -v
==27388== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

MemorySanitizer¶

compile 時加上參數 : -fsanitize=address

Example 1¶

前面用過的範例，再用一次

Source Code :

int *ptr;
__attribute__((noinline))
void FunctionThatEscapesLocalObject() {
    int local[100];
    ptr = &local[0];
}

int main(int argc, char **argv) {
    FunctionThatEscapesLocalObject();
    return ptr[argc];
}

Compile :

$ clang++ -O1 -g -fsanitize=memory -fno-omit-frame-pointer example.cpp -o example

Run :

$ ./example
==12719== WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x7f1030669d16 in main /tmp/example.cpp:11:9
    #1 0x7f102f17578f in __libc_start_main (/usr/lib/libc.so.6+0x300042078f)
    #2 0x7f1030615798 in _start (/tmp/example+0x35798)

SUMMARY: MemorySanitizer: use-of-uninitialized-value /tmp/example.cpp:11 main
Exiting

Algorithm¶

AddressSanitizer algorithm

Status¶

ASan¶

目前支援：

i386
i686
x86_64
ARM 32
ARM 64
MIPS
MIPS64
...

LSan¶

目前支援：

x86_64
MIPS64
MIPS64EL

compiler-rt/lib/lsan/lsan_common.cc 裡的 ScanRangeForPointers() 負責 memory scan

LSan on ARM only finds about 15% of leaks. The results are close to valgrind's on x86 so we decided to halt our work.

MSan¶

目前支援：

x86_64
MIPS64
MIPS64EL

TSan¶

目前支援：

x86_64
MIPS64
MIPS64EL

Sanitizer¶

Introduction¶

AddressSanitizer¶

Example 1¶

Example 2 (Can Not Detect) (Neither Valgrind ...)¶

Example 3 (Can Not Detect) (Valgrind can find it !!!)¶

Example 4 (Can Not Detect) (Valgrind can find it !!!)¶

MemorySanitizer¶

Example 1¶

Algorithm¶

Status¶

ASan¶

LSan¶

MSan¶

TSan¶

Reference¶