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SPOILER alert, literally: Intel CPUs afflicted with simple data-spewing spec-exec vulnerability
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 [...] 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."
[...] SPOILER, the researchers say, will make existing Rowhammer and cache attacks easier, and make JavaScript-enabled attacks more feasible – instead of taking weeks, Rowhammer could take just seconds. Moghimi said the paper describes a JavaScript-based cache prime+probe technique that can be triggered with a click to leak private data and cryptographic keys not protected from cache timing attacks.
Mitigations may prove hard to come by. "There is no software mitigation that can completely erase this problem," the researchers say. Chip architecture fixes may work, they add, but at the cost of performance.
(Score: 3, Interesting) by jmorris on Wednesday March 06 2019, @07:20PM
Speculative execution is what allowed Instructions Per Cycle to be greater than one, on the best current tech IPC is now around four. And also, as another commenter has already noted, speculative execution allows the CPU clock to greatly exceed the speed of the memory subsystem, without it the cpu would simply stall very quickly. So no, simply eliminating it is not a matter of a few percent loss in performance. If the simply issued a microcode update tomorrow to entirely disable it that 4GHz machine would suddenly be operating well under 1GHz comparable performance. The entire modern computer design would be called into question.
And yet nothing less is going to solve this problem. We are approaching a breaking point, something is going to have to yield.