Software systems are constantly evolving, with
new versions and patches being released on a continuous basis.
Unfortunately, software updates present a high risk, with many
releases introducing new bugs and security vulnerabilities.
We tackle this problem using a simple but effective multiversion
based approach. Whenever a new update becomes
available, instead of upgrading the software to the new version,
we run the new version in parallel with the old; by carefully
coordinating their executions and selecting the behavior of the
more reliable version when they diverge, we create a more
secure and dependable multi-version application.
We have implemented this technique in a prototype system
targeting multicore processors, and show that it can be applied
successfully to several security-critical applications, such as
lighttpd and redis.