Speculative execution, the practice of allowing processors to perform future work that may or may not be needed while they await the completion of other computations, is what enabled the Spectre vulnerabilities revealed early last year.
In a research paper distributed this month through pre-print service ArXiv, “SPOILER: Speculative Load Hazards Boost Rowhammer and Cache Attacks,” computer scientists at Worcester Polytechnic Institute in the US, and the University of Lübeck in Germany, describe a new way to abuse the performance boost.
The researchers – Saad Islam, Ahmad Moghimi, Ida Bruhns, Moritz Krebbel, Berk Gulmezoglu, Thomas Eisenbarth and Berk Sunar – have found that “a weakness in the address speculation of Intel’s proprietary implementation of the memory subsystem” reveals memory layout data, making other attacks like Rowhammer much easier to carry out.
The researchers also examined Arm and AMD processor cores, but found they did not exhibit similar behavior.
“We have discovered a novel microarchitectural leakage which reveals critical information about physical page mappings to user space processes,” the researchers explain.
“The leakage can be exploited by a limited set of instructions, which is visible in all Intel generations starting from the 1st generation of Intel Core processors, independent of the OS and also works from within virtual machines and sandboxed environments.”
The issue is separate from the Spectre vulnerabilities, and is not addressed by existing mitigations. It can be exploited from user space without elevated privileges.
“The root cause of the issue is that the memory operations execute speculatively and the processor resolves the dependency when the full physical address bits are available,” said Moghimi. “Physical address bits are security sensitive information and if they are available to user space, it elevates the user to perform other micro architectural attacks.”