Reorder Buffer Contention: A Forward Speculative Interference Attack for Speculation Invariant Instructions

Abstract

Speculative side-channel attacks access sensitive data and use transmitters to leak the data during wrong-path execution. Various defenses have been proposed to prevent such information leakage. However, not all speculatively executed instructions are unsafe: Recent work demonstrates that speculation invariant instructions are independent of speculative control-flow paths and are guaranteed to eventually commit, regardless of the speculation outcome. Compile-time information coupled with run-time mechanisms can then selectively lift defenses for speculation invariant instructions, reclaiming some of the lost performance.Unfortunately, speculation invariant instructions can easily be manipulated by a form of speculative interference to leak information via a new side-channel that we introduce in this paper. We show that forward speculative interference where older speculative instructions interfere with younger speculation invariant instructions effectively turns them into transmitters for secret data accessed during speculation. We demonstrate forward speculative interference on actual hardware, by selectively filling the reorder buffer (ROB) with instructions, pushing speculative invariant instructions in-or-out of the ROB on demand, based on a speculatively accessed secret. This reveals the speculatively accessed secret, as the occupancy of the ROB itself becomes a new speculative side-channel.

Hardware Security and Trust: Trends, Challenges, and Design Tools

“…These threats can be minimized at the designing and fabrication phases of the hardware lifecycle, but sometimes it can be inevitable to eliminate them completely due to the functionality expected by the hardware components and also due to some performance enhancing mechanisms used within the components. Secure boot attacks [23], [24], firmware attacks [25], [26], dynamic random access memory threats such as Row hammering attacks [27], [28], [29], cache attacks [30], [31], speculative execution attacks [32], [33], [34], [35] and code reuse attacks [36] are some examples for these types.…”

“…The channels used as covert channels are generally not meant for communications. Covert channel on Intel CPU-iGPU platform [34], cross-component covert channels on integrated CPU-GPU systems identified using the ring bus connecting CPU and GPU to the Last Level Cache (LLC) [35], conflict based cache covert channel exposed by reverse engineering cache behavior of PREFETCHNTA in Intel processors [36], covert channels created by exploiting vulnerabilities in current management mechanism in latest Intel processors [37] and covert channel exploitation of CVA6 RSC-V open-source CPU with the help of baremetal simulations [38] are some example works.…”