[Ksummit-2013-discuss] [ARM ATTEND] Trustzone-based security solution for ARM Linux

[Greg KH]

On Thu, Aug 15, 2013 at 11:44:30AM +0800, Barry Song wrote:
> For the moment, there is strong markting requirement from
> IVI(In-Vehicle Infotainment) or mobile to use ARM Trustzone. We take
> IVI as an example, Auto requires security enviorment to access CAN bus
> and other car busses. Auto requires security enviorment to show
> rearview/surround view from cameras and play alert audio. on the other
> hand, IVI system is generically working as a video streaming sink and
> HDMI sink instead of a source. To support HDCP and widevine, we need
> to make sure private keys and video buffers are only visible to
> security mode. With CAN stack, video playback backend and more tasks,
> generically it requires a multi-task RTOS running in security mode
> parallel with Linux in non-security mode.
> 
> Linux is a generic purpose OS with UI and all kinds of software, but
> we need to make sure even the Linux is ROOTed, RTOS in security mode
> is still active. We are able to find some opensource projects like
> SafeG[1], Multivisor[2], SierraVisor[3], but it turns out that ARM
> Linux has no rich support for this kind of architecture:
> 1. hypervisor running in monitor mode
> 2. RTOS running in security mode
> 3. Linux running in non-security mode

"Linux" is just a kernel, not a whole operating system :)

Anyway, why can't Linux be the RTOS kernel as well?  What are the
requirements for that kernel that Linux does not currently meet?

> So the point is that we need generic support for this, especially for
> IVI and other markets which want Trustzone technology a lot and have
> complex user scenarios.
> 1. Dispatch FIQ to security, dispatch IRQ to Linux, for this case, FIQ
> is not permitted to happen on Linux

Isn't that up to the hardware?  Nothing that Linux can do about that.

> 2. IPC support for communication between RTOS in security mode and
> Linux in non-security mode, as we need to communicate rich commands
> and buffers

What about using the virtual protocols we already have today for the
existing hypervisors?  Don't reinvent something new if you don't have
to.

> 3. as some CPU time is stolen by security mode, so the scheduler need
> to get this for load balance

Does the kernel know this time is gone?  Or is it not aware of it (like
MSIs on x86?)

thanks,

greg k-h