Leveraging 2.5D interposer technology, we advocate the integration of untrusted commodity components/chiplets with physically separate, entrusted logic components. Such organization provides a modern root of trust for secure system-level integration. We showcase our scheme by utilizing industrial ARM components that are interconnected via a security-providing active interposer, and thoroughly evaluate the achievable security via different threat scenarios. Finally, we provide detailed end-to-end physical design results to demonstrate the efficacy of our proposed methodology.