SMM/EL3 does work on Apple CPUs

By: Maynard Handley (name99.delete@this.name99.org), September 28, 2018 3:38 pm
Room: Moderated Discussions
I mentioned some days ago that I didn't know exactly how KPP (aka KTRR when implemented in HW on A10+) works. Well there is a hint as to how it works here:

https://xerub.github.io/ios/kpp/2017/04/13/tick-tock.html

The mechanism to get it running (and so scanning pages) is clearly baroque! And you can see why Apple moved to a HW scheme that does essentially the same thing as soon as possible.

But one additional thing this post reveals is that EL3 is absolutely functional (at least on pre-A10 CPUs). And this suggests that EL2 (hypervisor level) is likewise functional. This isn't THAT strange, but it's also not a slam-dunk; I could have believed that Apple had quietly just not bothered to implement EL2 and EL3 because why do so if you don't need them?
It also suggests that, IN PRINCIPLE, Apple could implement a hypervisor under iOS.
This is interesting IMHO not least for legal reasons --- you could imagine that if some country (that Apple cared about...) grew to absolutely insist that iPhones allow for alternative OSs because competition, Apple could in principle, I assume, insert in a hypervisor, provide some basic virtual drivers, and allow a Windows or a Linux or an Android to run alongside iOS?

And alternative version of the same idea could be something like (was it Samsung that did this?) providing two TOTALLY separated, no-communicating OS's, one for work and one personal use.

(Obviously both these ideas have some UI issues -- do both OS's get to support incoming phone calls or even just notifications, and how is that multiplexed on the screen?
But they do suggest interesting, albeit IMHO unlikely, possible evolutions.)
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SMM/EL3 does work on Apple CPUsMaynard Handley2018/09/28 03:38 PM
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