59 lines · c
1#include <sys/mman.h>2#include <signal.h>3#include <stdio.h>4#include <unistd.h>5 6enum {7 kMmapSize = 0x1000,8 kMagicValue = 47,9};10 11void *address;12volatile sig_atomic_t signaled = 0;13 14void handler(int sig)15{16 signaled = 1;17 if (munmap(address, kMmapSize) != 0)18 {19 perror("munmap");20 _exit(5);21 }22 23 void* newaddr = mmap(address, kMmapSize, PROT_READ | PROT_WRITE,24 MAP_ANON | MAP_FIXED | MAP_PRIVATE, -1, 0);25 if (newaddr != address)26 {27 fprintf(stderr, "Newly mmaped address (%p) does not equal old address (%p).\n",28 newaddr, address);29 _exit(6);30 }31 *(int*)newaddr = kMagicValue;32}33 34int main()35{36 if (signal(SIGSEGV, handler) == SIG_ERR)37 {38 perror("signal");39 return 1;40 }41 42 address = mmap(NULL, kMmapSize, PROT_NONE, MAP_ANON | MAP_PRIVATE, -1, 0);43 if (address == MAP_FAILED)44 {45 perror("mmap");46 return 2;47 }48 49 // This should first trigger a segfault. Our handler will make the memory readable and write50 // the magic value into memory.51 if (*(int*)address != kMagicValue)52 return 3;53 54 if (! signaled)55 return 4;56 57 return 0;58}59