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

[Robin Murphy]

On 01/03/18 14:15, Benjamin Gaignard wrote:
> 2018-03-01 15:02 GMT+01:00 Mark Rutland <mark.rutland@xxxxxxx>:
> > 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.