Intrinsic Rowhammer PUFs: Leveraging the Rowhammer effect for improved security

Physically Unclonable Functions (PUFs) have become an important and promising hardware primitive for device fingerprinting, device identification, or key storage. Intrinsic PUFs leverage components already found in existing devices, unlike extrinsic silicon PUFs, which are based on customized circuits that involve modification of hardware. In this work, we present a new type of a memory-based intrinsic PUF, which leverages the Rowhammer effect in DRAM modules - the Rowhammer PUF. Our PUF makes use of bit flips, which occur in DRAM cells due to rapid and repeated access of DRAM rows. Prior research has mainly focused on Rowhammer attacks, where the Rowhammer effect is used to illegitimately alter data stored in memory, e.g., to change page table entries or enable privilege escalation attacks. Meanwhile, this is the first work to use the Rowhammer effect in a positive context - to design a novel PUF. We extensively evaluate the Rowhammer PUF using commercial, off-the-shelf devices, not relying on custom hardware or an FPGA-based setup. The evaluation shows that the Rowhammer PUF holds required properties needed for the envisioned security applications, and could be deployed today.

I. Introduction

In recent years, attacks that exploit the Rowhammer effect have gained a lot of attention, as they can enable a plethora of security-related risks due to the wide-spread vulnerability imposed by the Rowhammer effect in today's DRAM modules. The phenomenon was first described by Kim et al. [1], who were able to induce so-called disturbance errors in high-density, commodity DRAM modules by repeatedly accessing uncached memory rows. Disturbance errors occur due to the charge coupling between DRAM cells, which accelerates charge leakage in adjacent rows, and eventually results in bits being flipped in so-called victim rows in DRAM, even though said victim rows were not explicitly accessed. The Rowhammer effect allows for breaking many software-based security mechanisms, as well as memory and process isolation, because it allows flipping memory bits, which would otherwise be protected by software-based access control mechanisms. Numerous papers have been published that use the Rowhammer effect in order to improve the identification of vulnerable DRAM cells or to implement various Rowhammer attacks [2]–[5].