CFFI support is not the only thing needed for PyPy. There is a severe issue in PyPy which prevents RestrictedPython from doing its restrictions. Thus through the web code cannot be secured when running on PyPy. (Anyone with access to the ZMI is able to write TTW code!) See https://github.com/zopefoundation/RestrictedPython/blob/master/docs/CHANGES.rst#40b1-2017-09-15 and https://bitbucket.org/pypy/pypy/issues/2653 for details.