pkru example

pkru.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <asm/prctl.h>
#include <sys/syscall.h>

#define PKEY_DISABLE_WRITE 0x1ull

int pkey_alloc(unsigned int flags, unsigned int access_rights) {
    return syscall(__NR_pkey_alloc, flags, access_rights);
}

int pkey_free(int pkey) {
    return syscall(__NR_pkey_free, pkey);
}

int pkey_mprotect(void *addr, size_t len, unsigned long prot, int pkey) {
    return syscall(__NR_pkey_mprotect, addr, len, prot, pkey);
}

void test_pkey_mprotect() {
    char *secret;
    secret = mmap(NULL, getpagesize(), PROT_WRITE | PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
    strncpy(secret, "The Magic Words are Squeamish Ossifrage.", 40);
    int real_prot = PROT_NONE;
    int pkey = pkey_alloc(0, PKEY_DISABLE_WRITE);
    int ret = pkey_mprotect(secret, getpagesize(), real_prot, pkey);
    printf("ret: %d\n", ret);
    printf("secret: %s\n", secret);
    pkey_free(pkey);
}

int main() {
    test_pkey_mprotect();
    return 0;
}

pkru.md

• Listing 5.9: Disabling Reads or Writes to the secret using MPK permissions.

gcc -o pkru pkru.c