[ARM ATTEND] Trustzone-based security solution for ARM Linux

[Barry Song]

2013/8/15 Ben Dooks <ben.dooks at codethink.co.uk>:
> On 15/08/13 04:44, 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.
>
>
> Personally, I just don't trust anything that is running on the main cpu
> not to get compromised in some form. There has been too little thought
> put in to securing these devices.

Trustzone is a hardware mechanism to stop as much as possible.

>
>
>> 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
>>
>> 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
>> 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
>> 3. as some CPU time is stolen by security mode, so the scheduler need
>> to get this for load balance
>
>
> With information being passed to the RTOS from the non-secure OS adds
> a method of attacking the secure world.

that doesn't matter. the hardware firewall for private keys storage
and memory based on trustzone will stop any people in non-security to
access them as hardware stops that.
you can get information as much as possible, for example, the base
address of video buffer, but you can't access it.


>
>
>> For IPC, RPMsg is kind of popular for commucating cross HMP. For
>> example, OMAP uses it as the IPC between M3 and A9; XilinX uses it as
>> IPC between two A9, one with FreeRTOS, the other one with Linux; ST-E
>> uses it to connect ARM with modem MCU. So we are also considering the
>> possibility to involve RPMsg as the backend for communication between
>> RTOS in security mode and Linux in non-security mode. then we get much
>> benefit from virtio, and some drivers will be usable directly.
>>
>> So for this topic, I want a presentation session with about 5 slides
>> to show the high-level architecture and requirement for a real and
>> complex Trustzone user case. Hoping we can get some rich support from
>> Linux for this architecture.
>>
>> On the other hand, if people can discuss Android mainlining project
>> more, i like much. for the moment, most Android patches have been
>> mainlined, but we still need to maintain both branches as there are
>> rebased patches from Google. So i want to get input about best
>> pratice.
>>
>> [1]SafeG (Safety Gate):
>> http://www.toppers.jp/en/safeg.html
>> [2]Green Hills Multivisor:
>> http://www.ghs.com/products/rtos/integrity_virtualization.html
>> [3]SierraVisor:
>> http://www.openvirtualization.org/
>
>
>
>
> --
> Ben Dooks                               http://www.codethink.co.uk/
> Senior Engineer                         Codethink - Providing Genius

-barry