Safe Virtual Execution Using Software Dynamic Translation

Safe virtual execution (SVE) allows a host computersystem to reduce the risks associated with runninguntrusted programs. SVE prevents untrusted programsfrom directly accessing system resources, thereby givingthe host the ability to control how individualresources may be used. SVE is used in a variety ofsafety-conscious software systems, including the JavaVirtual Machine (JVM), software fault isolation (SFI),system call interposition layers, and execution monitors.While SVE is the conceptual foundation for thesesystems, each uses a different implementation technology.The lack of a unifying framework for building SVEsystems results in a variety of problems: many usefulSVE systems are not portable and therefore are usableonly on a limited number of platforms; code reuseamong different SVE systems is often difficult or impossible;and building SVE systems from scratch can beboth time consuming and error prone.To address these concerns, we have developed a portable,extensible framework for constructing SVE systems.Our framework, called Strata, is based onsoftware dynamic translation (SDT), a technique formodifying binary programs as they execute. Strata isdesigned to be ported easily to new platforms and todate has been targeted to SPARC/Solaris, x86/Linux,and MIPS/IRIX. This portability ensures that SVEapplications implemented in Strata are available to awide variety of host systems. Strata also affords theopportunity for code reuse among different SVE applicationsby establishing a common implementationframework.Strata implements a basic safe virtual executionengine using SDT. The base functionality supplied bythis engine is easily extended to implement specific SVEsystems. In this paper we describe the organization ofStrata and demonstrate its extension by building twoSVE systems: system call interposition and stack-smashingprevention. To illustrate the use of the systemcall interposition extensions, the paper presents implementationsof several useful security policies.