[PATCH 0/3] STM32 Extended TrustZone Protection driver
benjamin.gaignard at linaro.org
Tue Feb 27 23:53:28 PST 2018
2018-02-27 20:46 GMT+01:00 Robin Murphy <robin.murphy at arm.com>:
> On 27/02/18 19:16, Benjamin Gaignard wrote:
>> 2018-02-27 18:11 GMT+01:00 Mark Rutland <mark.rutland at arm.com>:
>>> On Tue, Feb 27, 2018 at 03:09:23PM +0100, Benjamin Gaignard wrote:
>>>> On early boot stages STM32MP1 platform is able to dedicate some hardware
>>>> to a secure OS running in TrustZone.
>>>> We need to avoid using those hardware blocks on non-secure context (i.e.
>>>> because read/write access will all be discarded.
>>>> Extended TrustZone Protection driver register itself as listener of
>>>> BUS_NOTIFY_BIND_DRIVER and check, given the device address, if the
>>>> hardware block
>>>> could be used in a Linux context. If not it returns NOTIFY_BAD to driver
>>>> to stop driver probing.
>>> If these devices are not usable from the non-secure side, why are they
>>> not removed form the DT (or marked disabled)?
>>> In other cases, where resources are carved out for the secure side (e.g.
>>> DRAM carveouts), that's how we handle things.
>> That true you can parse and disable a device a boot time but if DT doesn't
>> exactly reflect etzpc status bits we will in trouble when try to get
>> access to
>> the device.
> Well, yes. If the DT doesn't correctly represent the hardware, things will
> probably go wrong; that's hardly a novel concept, and it's certainly not
> unique to this particular SoC.
>> Changing the DT is a software protection while etzpc is an hardware
>> so we need to check it anyway.
> There are several in-tree DT and code examples where devices are marked as
> disabled on certain boards/SoC variants/etc. because attempting to access
> them can abort/lock up/trigger a secure watchdog reset/etc. The only
> "special" thing in this particular situation is apparently that this device
> even allows its secure configuration to be probed from the non-secure side
> at all.
> Implementing a boardfile so that you can "check" the DT makes very little
> sense to me; Linux is not a firmware validation suite.
It is not about to "check" the DT but if Linux could get access to the hardware.
Hardware block assignment to secure or non-secure world could change at runtime
for example I2C block could be manage by secure OS for a trusted
application and when
it have finish "release" the it for Linux. I don't think that could be
done by changing DT.
I think that dhecking hardware blocks status bits before probe them is
also more robust than let
each driver discover at probe time that it hardware isn't responding.
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