You don't need OS to build a very precise clock for the purpose of exploiting timing attack. That's why SharedArrayBuffer[1] is disabled in all browsers. Moreo

You don't need OS to build a very precise clock for the purpose of exploiting timing attack. That's why SharedArrayBuffer[1] is disabled in all browsers. Moreover, not every side channel attack relies on timing attack. For interested readers, there is a paper titled "Fantastic Timers and Where to Find Them: High-Resolution Microarchitectural Attacks in JavaScript", which discussed a variety of ways to build high resolution clocks. [1]: https://security.stackexchange.com/questions/177033/how-can-sharedarraybuffer-be-used-for-timing-attacks https://security.stackexchange.com/questions/177033/how-can-...