In 2018, industry and academic researchers revealed a potentially devastating hardware flaw that made computers and other devices worldwide vulnerable to attack.

Researchers named the vulnerability Spectre because the flaw was built into modern computer processors that get their speed from a technique called "speculative execution," in which the processor predicts instructions it might end up executing and preps by following the predicted path to pull the instructions from memory. A Spectre attack tricks the processor into executing instructions along the wrong path. Even though the processor recovers and correctly completes its task, hackers can access confidential data while the processor is heading the wrong way.

Since Spectre was discovered, the world's most talented computer scientists from industry and academia have worked on software patches and hardware defenses, confident they've been able to protect the most vulnerable points in the speculative execution process without slowing down computing speeds too much.

They will have to go back to the drawing board.

A team of University of Virginia School of Engineering computer science researchers has uncovered a line of attack that breaks all Spectre defenses, meaning that billions of computers and other devices across the globe are just as vulnerable today as they were when Spectre was first announced. The team reported its discovery to international chip makers in April and will present the new challenge at a worldwide computing architecture conference in June.

The researchers, led by Ashish Venkat, William Wulf Career Enhancement Assistant Professor of Computer Science at UVA Engineering, found a whole new way for hackers to exploit something called a "micro-op cache," which speeds up computing by storing simple commands and allowing the processor to fetch them quickly and early in the speculative execution process. Micro-op caches have been built into Intel computers manufactured since 2011.

Venkat's team discovered that hackers can steal data when a processor fetches commands from the micro-op cache.

"Think about a hypothetical airport security scenario where TSA lets you in without checking your boarding pass because (1) it is fast and efficient, and (2) you will be checked for your boarding pass at the gate anyway," Venkat said. "A computer processor does something similar. It predicts that the check will pass and could let instructions into the pipeline. Ultimately, if the prediction is incorrect, it will throw those instructions out of the pipeline, but this might be too late because those instructions could leave side-effects while waiting in the pipeline that an attacker could later exploit to infer secrets such as a password."

Because all current Spectre defenses protect the processor in a later stage of speculative execution, they are useless in the face of Venkat's team's new attacks. Two variants of the attacks the team discovered can steal speculatively accessed information from Intel and AMD processors.

https://www.sciencedaily.com/releases/2021/04/210430165903.htm