Re: [PATCH 0/3] STM32 Extended TrustZone Protection driver
From: Robin Murphy
Date: Tue Feb 27 2018 - 14:46:40 EST
On 27/02/18 19:16, Benjamin Gaignard wrote:
2018-02-27 18:11 GMT+01:00 Mark Rutland <mark.rutland@xxxxxxx>:
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 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 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 core
to stop driver probing.
Huh?
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 protection
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.
Robin.