vmem/t_mprotect.c

/* t_mprotect.c

   Demonstrate the use of mprotect() to change the protection on
   a region of memory.

   This program is Linux-specific.
*/
#define _BSD_SOURCE         /* Get MAP_ANONYMOUS definition from <sys/mman.h> */
#include <sys/mman.h>
#include "tlpi_hdr.h"

#define LEN (1024 * 1024)

#define SHELL_FMT "cat /proc/%ld/maps | grep zero"
#define CMD_SIZE (sizeof(SHELL_FMT) + 20)
                            /* Allow extra space for integer string */

int
main(int argc, char *argv[])
{
    char cmd[CMD_SIZE];
    char *addr;

    /* Create an anonymous mapping with all access denied */

    addr = mmap(NULL, LEN, PROT_NONE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
    if (addr == MAP_FAILED)
        errExit("mmap");

    /* Display line from /proc/self/maps corresponding to mapping */

    printf("Before mprotect()\n");
    snprintf(cmd, CMD_SIZE, SHELL_FMT, (long) getpid());
    system(cmd);

    /* Change protection on memory to allow read and write access */

    if (mprotect(addr, LEN, PROT_READ | PROT_WRITE) == -1)
        errExit("mprotect");

    printf("After mprotect()\n");
    system(cmd);                /* Review protection via /proc/self/maps */

    exit(EXIT_SUCCESS);
}