Fun things

memory_fun.c

#include <malloc.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

int getnum1(int x) {
    x += 1;
    return x * x;
}

/*
int getnum2(int x) {
    x += 2;
    return x * x;
}
*/

static char *magicbuffer;

int main(void) {
    int pagesize;
    pagesize = sysconf(_SC_PAGE_SIZE);
    if (pagesize == -1) {
        printf("Sysconf error\n");
    }
    printf("Pagesize: %d\n", pagesize);
    magicbuffer = memalign(pagesize, 1 * pagesize);

    uint8_t magic[20] = {0x55, 0x48, 0x89, 0xe5, 0x89, 0x7d, 0xfc,
                         0x83, 0x45, 0xfc, 0x02, 0x8b, 0x45, 0xfc,
                         0x0f, 0xaf, 0x45, 0xfc, 0x5d, 0xc3};
    int (*func)(int) = &getnum1;
    printf("Num 1: %d\n", func(1));

    if (mprotect(magicbuffer, pagesize, PROT_READ | PROT_WRITE | PROT_EXEC) !=
        0) {
        printf("Setting memory protections failed\n");
    }

    memcpy(magicbuffer, magic, 20);
    func = (int (*)(int))magicbuffer;
    printf("Num 2: %d\n", func(1));

    return 0;
}