We recently proposed Start-Gap as a simple low-overhead mechanism to do near-perfect wear leveling in phase change memories. This method was extended to handle a malicious attack, Repeat Address Attack (RAA), and provided a lifetime of several months under such an attack. A recent study has argued that an attacker can use Birthday Paradox Attack (BPA) to cause much earlier failure of the Start-Gap method. The objective of this report is twofold. We first analyze the vulnerability of Start-Gap to BPA. We show that tuning the region size in our solution to handle both BPA and RAA causes a loss of lifetime of at most by 2x compared to a system that is tuned to handle only RAA. We then propose a practical framework, that can guarantee year(s) of lifetime under attacks while still incurring negligible (<1%) write overhead for typical applications. It uses a simple and novel Online Attack Detector (OAD) circuit to adapt wear leveling algorithm depending on the properties of the memory reference stream. The OAD circuit requires a hardware overhead of few tens of bytes and is quite effective at detecting a large family of attacks.
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