Adding a Kernel Module in base-hw

Franc sylvester sylvaster.franc at ...9...
Mon Jan 19 20:21:27 CET 2015

Hello Christian,

Thanks a lot for your reply. Essentially I want to demonstrate following
TrustZone scenario over the imx53 QSB board.

>> Now, I want to switch the control from Normal world OS (Genode) back to
>> the Secure world OS (Genode) by triggering(running a particular script
>> in Normal world). So what could be the right approach to achieve this
>> objective ?

>To switch to the secure world you can trigger a 'smc' assembler
>instruction, which will end up as a hypercall in the VMM. The 'smc'
>instruction needs to be executed in privileged mode (pl1 or higher).
>Therefore, if you want to trigger it via a script from userland, you
>need to create some kernel module first that executes the 'smc'


>From the above discussion as much i understood, It requires to add a kernel
module which will execute smc instruction and next it should be triggered
via a script from userland.


On Mon, Jan 19, 2015 at 4:18 PM, Christian Helmuth <
christian.helmuth at ...1...> wrote:

> Hello Franc,
> On Mon, Jan 19, 2015 at 03:34:06PM +0530, Franc sylvester wrote:
> > I am stuck at one point because of lack of understanding in Genode,
> > Actually I want to execute some assembly instruction in privileged mode
> in
> > base-hw kernel from a user script.
> >
> > So I need to know, How will I add a kernel module which will execute
> > assembly instruction and how can I call this module from the user space.
> >
> > And if there is already any such modules exist in Genode that will really
> > help me to understand the flow mechanism, Let me know.
> The answer to your question heavily depends on the task you address.
> From my point of view, it's better to stay away from any "general"
> solution to load code into the kernel resp. execute arbitrary
> instructions in kernel mode. At last, base-hw is a microkernel and
> should stay that way.
> To give an example, we extended base-hw for USB SOF interrupt
> filtering for the Raspberry Pi last autumn to highly reduce the impact
> on the system load. Therefore, we implemented a special case in the
> interrupt handling code
> The feature does not affect the kernel integrity as it just moves one
> single aspect of the driver into the kernel: Filter high-frequency
> interrupts that do not have to be handled in user mode. The kernel
> interrupt handler drops all incoming interrupts of the DWC device
> while the incoming frame number is smaller than the frame number
> scheduled by the user-level device driver.
> Could you provide us with more information about what you like to
> achieve? Is it really necessary to add a new system call? Would it be
> feasible to introduce an abstraction that solves the issue?
> Regards
> --
> Christian Helmuth
> Genode Labs
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