Re:Reading privileged memory with a side-channel
by aidenn0 on Wednesday January 03, 2018 @08:18PM
(#16067160)
That can't be right because they already round performance.now() so the Spectre attack didn't use it (it instead used a webworker with a tight-loop incrementing a counter)
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Re:Reading privileged memory with a side-channel
by olliej on Wednesday January 03, 2018 @09:07PM
(#16067417)
the tight loop iteration used a shared array buffer to provide a high resolution timer, specifically to deal with the obvious fix of truncating precision of performance.now().
The reason for /further/ truncating performance.now() is that the relative cost in this attack means that you don't need as much precision as was needed for the original (page table? I think) attack.
A SAB timer just needs to increment a counter in one thread and read it in the host thread and the granularity is however long it takes to get through a for-loop.