Cache Bypassing and Checkpointing to Circumvent Data Security Attacks on   STTRAM
  Spin-Transfer Torque RAM (STTRAM) is promising for cache applications. However, it brings new data security issues that were absent in volatile memory counterparts such as Static RAM (SRAM) and embedded Dynamic RAM (eDRAM). This is primarily due to the fundamental dependency of this memory technology on ambient parameters such as magnetic field and temperature that can be exploited to tamper with the stored data. In this paper we propose three techniques to enable error free computation without stalling the system, (a) stalling where the system is halted during attack; (b) cache bypass during gradually ramping attack where the last level cache (LLC) is bypassed and the upper level caches interact directly with the main memory; and, (c) checkpointing along with bypass during sudden attack where the processor states are saved periodically and the LLC is written back at regular intervals. During attack the system goes back to the last checkpoint and the computation continues with bypassed cache. We performed simulation for different duration and frequency of attack on SPLASH benchmark suite and the results show an average of 8% degradation in IPC for a one-time attack lasting for 50% of the execution time. The energy overhead is 2% for an attack lasting for the entire duration of execution. 
Nitin Rathi, Asmit De, Helia Naeimi and Swaroop Ghosh
cs.CR