run-shellcode.c

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <malloc.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>

#if __SIZEOF_LONG__ != 4
#error Build this as a 32-bit binary: use gcc -m32 ...
#endif

int
main(int ac, char **av)
{
  if (ac != 2) {
    printf("Usage: %s shellcode.bin\n", av[0]);
    exit(-1);
  }

  void *buf;
  int fd = open(av[1], O_RDONLY);
  if (fd < 0)
    perror("open");

  struct stat st;
  if (fstat(fd, &st) < 0)
    perror("fstat");

  buf = memalign(4096, st.st_size);
  if (!buf)
    perror("malloc");

  ssize_t cc = read(fd, buf, st.st_size);
  if (cc < 0)
    perror("read");
  if (cc != st.st_size)
    printf("incomplete read: %d %ld\n", cc, st.st_size);

  close(fd);

  if (mprotect(buf, st.st_size, PROT_READ|PROT_WRITE|PROT_EXEC) < 0)
    perror("mprotect");

  void (*f)(void) __attribute__((noreturn)) = buf;
  f();
}