Christophe Rippert

Protection in flexible operating system architectures

This paper presents our work concerning flexibility and protection in operating system kernels. In most existing operating systems, security is enforced at the price of flexibility by imposing protection models on the system programmer when building his system. We prove that flexibility can be preserved by separating the management of the protection policy from the tools used to enforce it. We present the secure software framework we have implemented in the THINK architecture to manage protection policies and guarantee they are carried out as specified. We then detail the elementary protection tools provided to the programmer so he can protect his system against unauthorized accesses and denial of service attacks. These tools are implemented in a policy-neutral way so as to guarantee their flexibility. Finally we validate our results by evaluating the flexibility of the protection provided on selected examples of dynamic modification of the protection policy.

ON-THE-FLY METADATA STRIPPING FOR EMBEDDED JAVA OPERATING SYSTEMS

Considering the typical amount of memory available on a smart card, it is essential to minimize the size of the runtime environment to leave as much memory as possible to applications. This paper shows that on-the-fly constant pool packing can result in a significant reduction of the memory footprint of an embedded Java runtime environment. We first present Jits, an architecture dedicated to building fully-customized Java runtime environments for smart cards. We then detail the op- timizations we have implemented in the class loading mechanism of Jits to reduce the size of the loaded class constant pool. By suppress- ing constant pool entries as they become unnecessary during the class loading process, we manage to compact constant pools of loaded classes to less than 8% of their initial size. We then present the results of our mechanism in term of constant pool and class size reductions, and conclude by suggesting some more aggressive optimizations.

THINK: a secure distributed systems architecture

In this paper, we present THINK, our distributed systems architecture, and the research we have conducted to provide the system programmer with an architecture he can use to build efficient and secure operating systems. By specifying and implementing elementary tools that can be used by the system programmer to implement a chosen security policy, we prove that flexibility can be guaranteed in an operating system without compromising security. Our work focuses on protection against denial of service attacks which compromise the system fairness in resource multiplexing and can cause the system to stall due to resource starvation.