linux-kernel - Re: [PATCH v2 0/2] STM32 Extended TrustZone Protection driver

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Date:   Thu, 1 Mar 2018 14:19:16 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Arnd Bergmann <arnd@...db.de>,
        Loic PALLARDY <loic.pallardy@...com>,
        devicetree@...r.kernel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Benjamin Gaignard <benjamin.gaignard@...com>
Subject: Re: [PATCH v2 0/2] STM32 Extended TrustZone Protection driver

On 01/03/18 14:15, Benjamin Gaignard wrote:
> 2018-03-01 15:02 GMT+01:00 Mark Rutland <mark.rutland@....com>:
>> On Thu, Mar 01, 2018 at 02:58:04PM +0100, Benjamin Gaignard wrote:
>>> On early boot stages STM32MP1 platform is able to dedicate some hardware blocks
>>> to a secure OS running in TrustZone.
>>> We need to avoid using those hardware blocks on non-secure context (i.e. kernel)
>>> because read/write accesses could generate illegale access exceptions.
>>>
>>> Extended TrustZone Protection driver make sure that device is disabled if
>>> non-secure world can't acces to it.
>>>
>>> version 2:
>>> - do not use notifier anymore
>>> - change status property value in device-tree if needed
>>> - use a list of phandle instead of hard coded array
>>
>> As mentioned on v1, I don't think this should be done in Linux at all.
>>
>> If you wish to handle this dynamically, please fixup the DT *before*
>> entering Linux.
>>
>> If you want a sane default in the dts file, put status = "disabled" on
>> all nodes which the secure world might take ownership of.
> 
> That is the case, nodes are disabled by ealier boot stages before entering
> in Linux but, since mistakes and/or errors are always possible, fixup the DT
> to avoid illegal access exceptions make sense for me.

So why not also run a test on the memory controller in case the 
bootloader made a mistake in the memory node too? As I mentioned before, 
if you can't trust the DT to describe your hardware correctly you've 
already lost.

Robin.