Faking deduplication to prevent timing side-channel attacks on memory deduplication

Content-based memory deduplication offers potential for saving physical memory by merging identical virtual pages. However, it also opens up a timing side-channel that allows attackers to probe whether an identical copy of one of their pages exists elsewhere on the system. This allows, for example, to find out what exact version of an application is being executed in another VM, and can also facilitate other side-channel attacks, e. g. some Rowhammer-based attacks. This paper presents FakeDD, a modification to Linux KSM, which uses fake deduplication as a countermeasure against such attacks that equalises the write times to duplicate and unique pages. Nevertheless, it still allows to make use of the memory savings offered by deduplication. FakeDD is available as open-source. It is evaluated with regard to its effectiveness and performance overhead. The results indicate that it can effectively prevent side-channel attacks based on the write time differences between duplicate and unique pages and that the additional performance overhead is smaller than that already incurred due to the standard KSM implementation and may thus be an acceptable trade-off for the additional security.