I occasionally wonder what an operating system running below ring 0 would be used for. I haven't thought of anything compelling, apart from being a backdoor.
Usually when I hear people talk about backdooring it's usually on the network stack. On a phone that would be a modem.
Most devices, even in your computer (eg: laptop battery) run an OS. There's a good talk somewhere on how we've lost our way with OS design and now need to write an OS that looks at a single machine as a distributed system.
LegoOS: A Disseminated, Distributed OS for
Hardware Resource Disaggregation ... We propose a new OS model called the splitkernel to
manage disaggregated systems. Splitkernel disseminates
traditional OS functionalities into loosely-coupled mon-
itors, each of which runs on and manages a hardware
component
Some batteries have an entire stm32 series microcontroller in them, I've seen battery controllers that are actually the same "CPU" as on a discrete single motor quadcopter ESC.
Apple's laptop batteries in 2008 MacBook models have an independent microcontroller in them, which enables apple to manage it at a much more advanced level.
That generation of laptops can detect a problem with the battery much earlier (e.g. It can warn the user a year before the battery starts to swell. Been there, seen that). This knowledge is the basis of apple's battery technology that we see on their mobiles (iOS and macOS) today.
IIRC the password on these things were set to a default one and a PoC exploit was written for that platform.
MicroSD cards have a fully functional 32-bit microcontroller in them, it manages the write leveling and bad sector mitigation, but it's a fully fledged CPU otherwise.
Even when sending encrypted texts with Signal, I can't help but wonder if the keyboard software is sending everything to a government entity. Or, if a piece of hardware can silently grab screenshots.
Supposedly, it’s for low level system management functions. As in, stuff that could be done in hardware, but doing it in software is easier. Kindof like System Management Mode (SMM), but even lower.
