This is vmem/t_mprotect.c (Listing 50-1, page 1046), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* 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 */
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)

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

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

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

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

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



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