[TZ_VMM] - i.MX53 QSB

[Stefan Kalkowski]

Hello Tiago,

On 05/25/2016 04:56 PM, Tiago Brito wrote:
> Hi, I have an i.MX53 QSB development board and I want to experiment with
> ARM TrustZone.
> 
> I'm a beginner with regards to genode and kernel development in general.
> 
> I was able to run tz_vmm on the QSB and interact with the linux which runs
> in normal world. What I want to do next is a fairly simple system where
> inside linux I can call an SMC and switch to the secure world, then whilst
> in secure world print something (like "Hello From Secure World" and also
> print some argument from the normal world) and then go back to linux.
> 
> I have read some of the messages in the mailing list and I noticed some of
> you (other mailing list subscribers) already achieved similar communication
> protocols but because I'm new to genode I don't know where to start.

Well, the very first pointer to gain more understanding of this concrete
scenario ist to read the detailed documentation of it:

  http://genode.org/documentation/articles/trustzone

Most of your questions, e.g., how to build the Linux kernel?, or is it a
modified Linux kernel? are already answered there.

> 
> I know I probably have to create a kernel module for the linux running in
> normal world so I can call SMC from a userspace application, but I don't
> know how to do that since I don't see where the linux is being compiled for
> genode [1]. Do I have to compile another linux? How do I incorporate this
> new linux version to work with genode?

Actually the Linux kernel version you are using when executing the
tz_vmm run-script already issues SMC calls that switch to the secure
world, where the VMM handles those calls and afterwards returns to the
normal world.

> 
> Besides this I also don't know where to start modifying tz_vmm in order to
> achieve my goals. I know where tz_vmm's code is but I don't know where to
> start changing it. I have also seen some mailing list questions regarding
> the world switch from secure world to normal world. It seems that from
> normal to secure you should call an SMC, but from secure to normal the
> monitor mode implementation cannot handle entries from the secure world and
> thus no SMC can be called directly [2].

The typical activity flow is:

 * Linux kernel issues an SMC call, e.g., to tell the VMM where its
   framebuffer is located in physical memory [1]
 * the HW kernel of Genode receives an exception, pauses the Linux VM,
   and delivers a signal to the related VMM [2]
 * the VMM receives the signal that the VM got paused due to an SMC
   call [3]
 * the VMM informs the HW kernel that the VM should be executed again
   after handling the call [4]
 * next time the scheduler of the HW kernel chooses the VM, it issues a
   world-switch to it [5]

Regards
Stefan

[1]
https://github.com/skalk/linux/blob/bc1707a23a9770cf080a1b87b4f553a2a39ac636/drivers/video/mxc/mxc_ipuv3_fb.c#L339
[2]
https://github.com/genodelabs/genode/blob/master/repos/base-hw/src/core/spec/arm_v7/trustzone/kernel/vm.cc#L52
[3]
https://github.com/genodelabs/genode/blob/master/repos/os/src/server/tz_vmm/spec/imx53/main.cc#L95
[4]
https://github.com/genodelabs/genode/blob/master/repos/os/src/server/tz_vmm/spec/imx53/main.cc#L119
[5]
https://github.com/genodelabs/genode/blob/master/repos/base-hw/src/core/spec/arm_v7/trustzone/kernel/vm.cc#L72

> 
> Can you give my some feedback on how to achieve these things on the i.MX53
> QSB?
> 
> Thanks in advance, Tiago
> 
> [1] - https://sourceforge.net/p/genode/mailman/message/33244107/
> [2] - https://sourceforge.net/p/genode/mailman/message/34244066/
> 
> 
> 
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-- 
Stefan Kalkowski
Genode Labs

http://www.genode-labs.com/ · http://genode.org/