Replace space in string to underscore w/ x86_64 shellcode in Python.

replace_space_to_underscore.py

import ctypes
import mmap


def replace_space_to_underscore(input_: str):
    assert input_.isascii()
    buf = ctypes.create_string_buffer(input_.encode())
    shellcode = (
        b"\x48\xbf"
        + ctypes.addressof(buf).to_bytes(8, "little")
        + b"\x48\xbe"
        + len(input_).to_bytes(8, "little")
        + b"\x48\x89\xf1\x48\x85\xc9\x74\x10\x80\x3f\x20\x75\x03\xc6\x07\x5f\x48\xff\xc7\x48\xff\xc9\x75\xf0\xc3"
    )
    mem = mmap.mmap(
        -1,
        mmap.PAGESIZE,
        mmap.MAP_SHARED,
        mmap.PROT_READ | mmap.PROT_WRITE | mmap.PROT_EXEC,
    )
    mem.write(shellcode)
    addr = int.from_bytes(ctypes.string_at(id(mem) + 16, 8), "little")
    functype = ctypes.CFUNCTYPE(ctypes.c_void_p)
    fn = functype(addr)
    fn()
    return buf.value.decode()


print(replace_space_to_underscore("Back to python!"))