OpenBSD disables Intel Hyper-Threading due to security concerns

Posted on Thursday, June 21 2018 @ 13:55 CEST by Thomas De Maesschalck
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OpenBSD made the unusual decision to turn off Intel's Hyper-Threading by default. Developer Mark Kettenis reports this is a security measure to protect users against possible Spectre-class exploits. There's no evidence for such attacks, but OpenBSD believes Intel's multi-threading implementation can make attacks a lot easier because TLBs and L1 caches are shared between threads.
“This can make cache timing attacks a lot easier and we strongly suspect that this will make several Spectre-class bugs exploitable.”

So OpenBSD has decided to disable Intel CPU hyper-threading, with “a new hw.smt sysctl,” in order to avoid data potentially leaking from applications to other software via Spectre-like processor flaws.
The performance impact depends on the use case. Some applications benefit hugely from Hyper-Threading, while other workloads actually see a performance hit. A lot depends on software optimizations, and not everything is suitable for parallelization.

The measure isn't limited to Intel CPUs. Kettenis writes OpenBSD plans to extend the feature to CPUs from other vendors and other hardware architectures.


About the Author

Thomas De Maesschalck

Thomas has been messing with computer since early childhood and firmly believes the Internet is the best thing since sliced bread. Enjoys playing with new tech, is fascinated by science, and passionate about financial markets. When not behind a computer, he can be found with running shoes on or lifting heavy weights in the weight room.



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