ldst

/* self modifying code */

#include <stdio.h>
#include <memory.h>
#include <sys/mman.h>

#include <stdlib.h>
#include <stdarg.h>
#include <unistd.h>

unsigned char payload[] = { 0x68, 0xDE, 0xAD, 0xBE, 0xEF, 0xC3 };

unsigned int hook_function[256];
int hook_cur = 0;

int
fake_printf(char* fmt, ...)
{
    puts("Fake #1");
    puts( fmt );
}

void
fakeLDST(void* function, void* fake)
{
    int i;
    unsigned page = (unsigned)function & ~( getpagesize() - 1 );
    unsigned int vaddr = (unsigned int)function;
    unsigned int raddr = (unsigned int)fake;

    mprotect( (char*)page, getpagesize(), PROT_READ | PROT_WRITE | PROT_EXEC );

    memcpy( payload + 1, &raddr, sizeof(int) );

    memcpy( (void*)vaddr, payload, 6 );
}

void
saveLD(void* function, void* saved)
{
    int i;

    if(!saved)
        saved = malloc ( 16 );

    for(i = 0;i < 16;i++)
        *(unsigned char*)(saved + i) = *(unsigned char*)(function + i);
}

void
restoreLD(void* function, void* saved)
{
    int i;

    for(i = 0;i < 16;i++)
        *(unsigned char*)(function + i) = *(unsigned char*)(saved + i);
}

int
main(int argc, char** argv)
{
    void* old_printf = NULL;

    saveLD( &printf, &old_printf );

    fakeLDST( &printf, &fake_printf );

    printf("LOL(0x%x)\n", &fake_printf);

    restoreLD( &printf, &old_printf );

    printf("LOL(0x%x)\n", &fake_printf);

    exit( 0 );

    return 0;
}