PyQBDIPreload

PyQBDIPreload is an implementation of QBDIPreload for PyQBDI. It allows users to inject the Python runtime into a target process and execute their own script in it. The limitations are pretty much the same as those we face on QBDIPreload and PyQBDI:

  • Only Linux and macOS are currently supported

  • The executable should be injectable with LD_PRELOAD or DYLD_INSERT_LIBRARIES

  • PyQBDIPreload cannot be injected in a Python process

  • The Python runtime and the target must share the same architecture

  • An extra VM must not be created. An already prepared VM is provided to pyqbdipreload_on_run().

Note

The Python library libpython3.x.so must be installed.

Main hook process

Unlike QBDIPreload, the hook of the main function cannot be customised so you are unable to alter the hook process. The Python interpreter is only initialised once the main function is hooked and the script is loaded. Furthermore, some modifications are made on the environment of the interpreter before the user script loading:

  • sys.argv are the argument of the executable

  • LD_PRELOAD or DYLD_INSERT_LIBRARIES are removed from os.environ

  • pyqbdi.__preload__ is set to True

Instrumentation

Once the script is loaded, the pyqbdipreload_on_run() function is called with a ready-to-run VM. Any user callbacks should be registered to the VM, then the VM can be run with pyqbdi.VM.run().

import pyqbdi

def instCallback(vm, gpr, fpr, data):
    # User code ...
    return pyqbdi.CONTINUE

def pyqbdipreload_on_run(vm, start, stop):
    vm.addCodeCB(pyqbdi.PREINST, showInstruction, None)
    vm.run(start, stop)

Exit hook

The atexit module is triggered when the execution is finished, or when exit or _exit are called.

Note

Any VM object is invalided when the atexit module is triggered and should never be used.

Execution

A script called pyqbdipreload.py is brought to set the environment up and run the executable. The first parameter is the PyQBDIPreload script. Next are the binary followed by its respective arguments if any.

python3 -m pyqbdipreload <script> <executable> [<arguments> ...]

Full example

Merging everything we have learnt throughout this tutorial, we are now able to write our Python script which prints the instructions that are being executed by the target executable.

#!/usr/bin/env python3

import pyqbdi

def insnCB(vm, gpr, fpr, data):
    instAnalysis = vm.getInstAnalysis()
    print("0x{:x}: {}".format(instAnalysis.address, instAnalysis.disassembly))
    return pyqbdi.CONTINUE


def pyqbdipreload_on_run(vm, start, stop):
    vm.addCodeCB(pyqbdi.PREINST, showInstruction, None)
    vm.run(start, stop)