The majority of smartphones either run iOS or Android operating systems. This has created two distinct ecosystems largely controlled by Apple and Google - they dictate which applications can run, how they run, and what kind of phone resources they can access. Barring some exceptions in Android where different phone manufacturers may have influence, users, developers, and governments are left with little control. Specifically, users need to entrust their security and privacy to OS vendors and accept the functionality constraints they impose. Given the wide use of Android and iOS, immediately leaving these ecosystems is not practical, except in niche application areas. In this work, we propose a new smartphone architecture that securely transfers the control over the smartphone back to the users while maintaining compatibility with the existing smartphone ecosystems. Our architecture, named TEEtime, is based on ARMv8 and implements novel, TEE-based, resource and interrupt isolation mechanisms which allow the users to flexibly choose which resources (including peripherals) to dedicate to different isolated domains, namely, to legacy OSs and to user's proprietary software. We show the feasibility of our design by implementing a prototype of TEEtime on an ARM emulator
