4 ms·

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.

colejohnson66 4y ago
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.
rsync 4y ago
The SIM card in your mobile telephone is doing that right now. You are correct - it is basically used as a back door.
- _ktx2 4y ago
  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.
  - walrus01 4y ago
    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.
    - bayindirh 4y ago
      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.
      - nousermane 4y ago
        IBM PC keyboard from 1981 (and all later external PC & Mac keyboards) have an independent microcontroller. https://en.wikipedia.org/wiki/Intel_MCS-48#Uses https://en.wikipedia.org/wiki/Intel_MCS-48#Uses
    - gambiting 4y ago
      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.
      - bayindirh 4y ago
        And, there's a couple of great write-ups about them [0][1]. [0]: https://www.bunniestudios.com/blog/?p=3554 https://www.bunniestudios.com/blog/?p=3554 [1]: https://i.blackhat.com/us-18/Wed-August-8/us-18-Valadon-Reversing-a-Japanese-Wireless-SD-Card-From-Zero-to-Code-Execution.pdf https://i.blackhat.com/us-18/Wed-August-8/us-18-Valadon-Reve...
  - rwmj 4y ago
    Is it this one? https://www.youtube.com/watch?v=36myc8wQhLo https://www.youtube.com/watch?v=36myc8wQhLo USENIX ATC '21/OSDI '21 Joint Keynote Address-It's Time for Operating Systems to Rediscover Hardware Edit or this one (not a talk but a paper)? https://www.usenix.org/system/files/osdi18-shan.pdf https://www.usenix.org/system/files/osdi18-shan.pdf 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
    - kodah 4y ago
      Similar enough! The one that I'm thinking of was the only actual non Linux talk (and really, OS development talk) at a OS Dev conference.
  - Terry_Roll 4y ago
    > and now need to write an OS that looks at a single machine as a distributed system Exactly, currently they are too easily exploitable because they are not joined up. You see it with gpu's being hacked and the OS not recognising this.
- walrus01 4y ago
  And the radio baseband firmware, what the hell is going on in there is likely known only to Qualcomm and the nsa.
  - deusum 4y ago
    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.
Avery3R 4y ago
ring -1 is canonically the hypervisor, so you could probably count hyper-v or xen or esxi as operating systems

colejohnson66 4y ago

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.

rsync 4y ago

The SIM card in your mobile telephone is doing that right now. You are correct - it is basically used as a back door.

_ktx2 4y ago
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.
- walrus01 4y ago
  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.
  - bayindirh 4y ago
    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.
    - nousermane 4y ago
      IBM PC keyboard from 1981 (and all later external PC & Mac keyboards) have an independent microcontroller. https://en.wikipedia.org/wiki/Intel_MCS-48#Uses https://en.wikipedia.org/wiki/Intel_MCS-48#Uses
  - gambiting 4y ago
    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.
    - bayindirh 4y ago
      And, there's a couple of great write-ups about them [0][1]. [0]: https://www.bunniestudios.com/blog/?p=3554 https://www.bunniestudios.com/blog/?p=3554 [1]: https://i.blackhat.com/us-18/Wed-August-8/us-18-Valadon-Reversing-a-Japanese-Wireless-SD-Card-From-Zero-to-Code-Execution.pdf https://i.blackhat.com/us-18/Wed-August-8/us-18-Valadon-Reve...
- rwmj 4y ago
  Is it this one? https://www.youtube.com/watch?v=36myc8wQhLo https://www.youtube.com/watch?v=36myc8wQhLo USENIX ATC '21/OSDI '21 Joint Keynote Address-It's Time for Operating Systems to Rediscover Hardware Edit or this one (not a talk but a paper)? https://www.usenix.org/system/files/osdi18-shan.pdf https://www.usenix.org/system/files/osdi18-shan.pdf 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
  - kodah 4y ago
    Similar enough! The one that I'm thinking of was the only actual non Linux talk (and really, OS development talk) at a OS Dev conference.
- Terry_Roll 4y ago
  > and now need to write an OS that looks at a single machine as a distributed system Exactly, currently they are too easily exploitable because they are not joined up. You see it with gpu's being hacked and the OS not recognising this.
walrus01 4y ago
And the radio baseband firmware, what the hell is going on in there is likely known only to Qualcomm and the nsa.
- deusum 4y ago
  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.

Avery3R 4y ago

ring -1 is canonically the hypervisor, so you could probably count hyper-v or xen or esxi as operating systems