Data Privacy in Non-Volatile Cache: Challenges, Attack Models and Solutions

Spin-Transfer-Torque RAM (STTRAM) is considered to be a strong candidate for last level cache (LLC). Although promising STTRAM LLC brings new security challenges that were absent in conventional volatile memories such as Static RAM (SRAM). The root cause is persistent data and the fundamental dependency of the memory technology on ambient parameters such as magnetic field and temperature that can be exploited to compromise the data. We provide a qualitative analysis of the data privacy issues in the emerging nonvolatile cache. We also propose new attack models to compromise the sensitive data in LLC. The encryption technique used to secure data in main memory and hard disk may not be useful for LLC due to latency overhead. We propose two low-overhead techniques to ensure data privacy in LLC-(a) implementing semi nonvolatile memory (SNVM); and, (b) data erasure at power OFF. Erasing could be energy intensive and may require dedicated battery to work under power failure attacks. To address this concern we reuse the energy stored in power rail after power OFF to erase the bits using a canary circuit to track MTJ write time. The simulation results show 0.6% IPC loss and 1.2% energy overhead during normal operation due to added circuitry.