Evaluating Hard Object: a Lightweight Module Isolation System

Because large, complex systems inevitably contain se-curity vulnerabilities, it is important to mitigate their impact. One of the most effective methods for doing so is privilege separation, the separation of an application into modules such that the compromise of one module grants the attacker only the limited privileges possessed by that module. However, the traditional hardware ad-dress space mechanism used to isolate processes exhibits high communication overhead between modules, mak-ing it impractical for fine-grained privilege separation. Software-based fault isolation (SFI) largely eliminates communication overhead, but provides less effective iso-lation and imposes substantial complexity and runtime overhead. Hard Object, a hybrid hardware/software solution, achieves the best of both worlds by providing a model similar to SFI but performing the most expensive op-erations in simple hardware extensions. The system, designed as an extension of a 32-bit x86 PC platform, is language-agnostic, and provides strong guarantees suit-able for isolating malicious code. In this report, we present details of an (incomplete) reference implemention of Hard Object based on the cycle-accurate 32-bit x86 simulator PTLSim[11]; a com-panion document that accompanies this submission presents the full details of the design. Additionally, we provide an evaluation of a modularized passwd application run-ning on our modified simulator. For this application, we see a slowdown of 2.6 % as compared to a reference implementation running on the unmodified simulator. In the future we plan to complete the simulator and evaluate a more comprehensive set of applications. 1