4 ms·
Just terminology. Whenever a new higher-privileged entity is created, it is sometimes described as a negative ring. There was a time when people thought if we
by ngneer 2y ago
Just terminology. Whenever a new higher-privileged entity is created, it is sometimes described as a negative ring.
There was a time when people thought if we could put the secure code in a lower ring, then with it we could protect the rest of the system. With virtualization, the hypervisor is in ring -1, which is technically not a ring, but rather a mode called VMX root operation, post-VMXON. This enables things like the blue pill attack, where the hypervisor is itself presented with a false image of the underlying physical hardware, by a malicious layer. You can find the same pattern in ARM TrustZone, where the secure code is repeatedly broken.
"if only we had ring -N"
- dwoldrich 2y agoCrazy complexity. Mind blown!
- Dalewyn 2y agoIt's the same reason that the nominal thrust level on the Space Shuttle Main Engines is 104.5%[1]. No, not 100% (it was originally), 104.5%. Why? Because you don't go back and change all your rules and documentation following subsequent developments in the field, that causes unnecessary confusion and errors down the road. [1]: https://en.wikipedia.org/wiki/RS-25#Engine_throttle/output https://en.wikipedia.org/wiki/RS-25#Engine_throttle/output
- ngneer 2y agoLikewise. Engineers do not idle well.