Re: This is news?
> The idea of monitoring some parameter of the chip to infer what it is doing, rather than trying to steal the data from the processing stream directly, has been around for decades at least. I messed around with it a little bit in the 1990's for fun
This.
To use the always-popular car analogy, this is a bit like installing a microphone inside the engine bay.
By listening to the engine, you'd be able to build up a picture of the engine's revs, as well as things like gear changes, etc.
And from that, you'd be able to build up a map of where the car has travelled to.
E.g. high revs for two minutes, followed by idling for 30 seconds: drove 0.75 miles down the road, stopped at traffic lights.
It wouldn't be particularly precise, but over time - as per exploits like this - you'd be able to create a pretty good model.
Fundamentally, any activity which produces detectable side-effects can be passively monitored, and data extracted from that monitoring. There's even been exploits which listen to PSU fan speeds, as that's a sign the CPU is pulling more power...
The trick is to minimise these side effects and/or restrict access to them.