linux-kernel - Re: [PATCH v2 0/7] Introduce bus firewall controller framework

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Date:   Tue, 28 Jan 2020 16:36:28 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Benjamin Gaignard <benjamin.gaignard@...com>
Cc:     broonie@...nel.org, robh@...nel.org, arnd@...db.de,
        shawnguo@...nel.org, s.hauer@...gutronix.de, fabio.estevam@....com,
        lkml@...ux.net, loic.pallardy@...com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-imx@....com,
        kernel@...gutronix.de, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, system-dt@...ts.openampproject.org,
        stefano.stabellini@...inx.com, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v2 0/7] Introduce bus firewall controller framework

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