On Tue, Jan 28, 2020 at 04:37:59PM +0100, Benjamin Gaignard wrote:

Bus firewall framework aims to provide a kernel API to set the configuration
of the harware blocks in charge of busses access control.

Framework architecture is inspirated by pinctrl framework:
- a default configuration could be applied before bind the driver.
  If a configuration could not be applied the driver is not bind
  to avoid doing accesses on prohibited regions.
- configurations could be apllied dynamically by drivers.
- device node provides the bus firewall configurations.

An example of bus firewall controller is STM32 ETZPC hardware block
which got 3 possible configurations:
- trust: hardware blocks are only accessible by software running on trust
  zone (i.e op-tee firmware).
- non-secure: hardware blocks are accessible by non-secure software (i.e.
  linux kernel).
- coprocessor: hardware blocks are only accessible by the coprocessor.
Up to 94 hardware blocks of the soc could be managed by ETZPC.

/me confused. Is ETZPC accessible from the non-secure kernel space to
begin with ? If so, is it allowed to configure hardware blocks as secure
or trusted ? I am failing to understand the overall design of a system
with ETZPC controller.

At least two other hardware blocks can take benefits of this:
- ARM TZC-400: http://infocenter.arm.com/help/topic/com.arm.doc.100325_0001_02_en/arm_corelink_tzc400_trustzone_address_space_controller_trm_100325_0001_02_en.pdf
  which is able to manage up to 8 regions in address space.

I strongly have to disagree with the above and NACK any patch trying
to do so. AFAIK, no system designed has TZC with non-secure access.
So we simply can't access this in the kernel and hence need no driver
for the same. Please avoid adding above misleading information in future.

--
Regards,
Sudeep


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