Editing Hyper-threading (section)

== Security ==
In May 2005, [[Colin Percival]] demonstrated that a malicious thread on a Pentium&nbsp;4 can use a timing-based [[side-channel attack]] to monitor the [[memory access pattern]]s of another thread with which it shares a cache, allowing the theft of cryptographic information. This is not actually a [[timing attack]], as the malicious thread measures the time of only its own execution. Potential solutions to this include the processor changing its cache eviction strategy or the operating system preventing the simultaneous execution, on the same physical core, of threads with different privileges.<ref>{{cite web
 | url = http://www.daemonology.net/papers/htt.pdf
 | title = Cache Missing for Fun and Profit
 | date = 2005-05-14 | access-date = 2016-06-14
 | first = Colin | last = Percival | website = Daemonology.net
}}</ref> In 2018 the [[OpenBSD]] operating system has disabled hyper-threading "in order to avoid data potentially leaking from applications to other software" caused by the [[Foreshadow (security vulnerability)|Foreshadow/L1TF]] vulnerabilities.<ref>{{Cite news|url=https://www.theregister.co.uk/2018/06/20/openbsd_disables_intels_hyperthreading/|title=OpenBSD disables Intel's hyper-threading over CPU data leak fears|access-date=2018-08-24}}</ref><ref>{{Cite web|url=https://marc.info/?l=openbsd-tech&m=153504937925732&w=2|title='Disable SMT/Hyperthreading in all Intel BIOSes' - MARC|website=marc.info|access-date=2018-08-24}}</ref> In 2019 a [[Microarchitectural Data Sampling|set of vulnerabilities]] led to security experts recommending the disabling of hyper-threading on all devices.<ref name="Greenberg">{{cite news|author1-first=Andy|author1-last=Greenberg|url=https://www.wired.com/story/intel-mds-attack-speculative-execution-buffer/|title=Meltdown Redux: Intel Flaw Lets Hackers Siphon Secrets from Millions of PCs|newspaper=[[WIRED]]|date=14 May 2019|access-date=14 May 2019}}</ref>