Multi-version Execution Techniques for Increasing the Reliability and Security of Evolving Software

One of the distinguishing characteristics of software systems is that they evolve: new patches are committed to software repositories and new versions are released to users on a continuous basis. Unfortunately, many of these changes bring unexpected failures that break the stability of the system or affect its security, and users face the uncomfortable choice between using an old stable version which misses recent features and bug fixes, and upgrading to a new version which improves the software in certain ways, only to introduce other bugs and security vulnerabilities.
 In this fellowship, I plan to investigate novel techniques for improving the reliability and security of evolving software, based on the idea of combining the execution of multiple software versions in such a way as to increase the reliability and security of the "multi-version" application and eliminate a large number of common bugs introduced by software updates.
 This is an ambitious proposal, which presents several challenges spanning the areas of software engineering, computer systems, and security: understanding how software evolves, and particularly the effects of incorrect updates on software evolution; addressing the technical challenges of multi-version execution such as creating an application-level sandboxing environment and devising lightweight record and replay techniques; designing error recovery strategies that effectively combine different software versions; and determining the applicability of multi-version execution to the different types of applications and code changes encountered in practice.