The unprecedented growth of computing power and communication bandwidth in the last few decades has driven an explosion in the size and complexity of application software. Specifically, it has spurred an almost universal adoption of modular and extensible software designs, from ordinary PC applications, to operating systems kernels, and even to embedded systems. In many cases, however, the ability to extend software systems has come hand in hand with the need to isolate them from untrusted or potentially faulty extensions. This dissertation will focus on the important problem of code isolation, where existing techniques vary in many and often interrelated dimensions such as granularity, code complexity, invocation latency, dynamism, isolation strategy, permissible extension functionality, and degree of integration with the operating system kernel. Specifically, the implementation of a particular technique imposes restrictions on the properties of extensions. Examples include proof-based techniques that are only applicable to simple extensions of small granularity, hardware-based isolation techniques that typically incur a measurable invocation latency due to hardware re-configuration overhead, and programming language techniques that impose implementation and compiler restrictions. The goal of this dissertation is to explore the design space of code isolation techniques, identify characteristics of individual approaches, and then argue for and design a hybrid approach that combines their advantages while avoiding their drawbacks. The contributions of this thesis will be threefold: (1) a taxonomy of metrics and properties relevant to software code isolation techniques, (2) the design and implementation of a novel hybrid architecture for safe kernel extension with pliable characteristics, and (3) an evaluation of the hybrid approach and comparison with homogeneous alternatives.

Code modularization provides benefits throughout the software life cycle; however, the presence of crosscutting concerns (CCCs) in software hinders its complete modularization. This thesis describes IVCon, a GUI-based tool that provides a novel approach to modularization of CCCs. IVCon enables users to create, examine, and modify their code in two different views, the woven view and the unwoven view. The woven view displays program code in colors that indicate which CCCs various code segments implement. The unwoven view displays code in two panels, one showing the core of the program and the other showing all the code implementing each concern in an isolated module. IVCon aims to provide an easy-to-use interface for conveniently creating, examining, and modifying code in, and translating between, the woven and unwoven views.