[U-Boot] [PATCH 0/2] Fix CAAM for TrustZone enable for warp7

[Auer, Lukas]

On Wed, 2018-01-24 at 14:35 +0000, Bryan O'Donoghue wrote:
> 
> On 24/01/18 12:52, Auer, Lukas wrote:
> > On Tue, 2018-01-23 at 21:10 +0000, Bryan O'Donoghue wrote:
> > > This series is the u-boot fix to a problem we encountered when
> > > enabling
> > > OPTEE/TrustZone on the WaRP7. The symptom is once TrustZone is
> > > activated
> > > the first page of CAAM registers becomes read-only, read-zero
> > > from
> > > the
> > > perspective of Linux and other non TrustZone contexts.
> > > 
> > > Offlining the problem with Peng Fan[1] we eventually came to
> > > realise
> > > the
> > > problem could be worked around by
> > > 
> > > 1. Making Linux skip RNG initialisation - a set of patches should
> > > be
> > >     hitting LKML to do just that.
> > > 
> > > 2. Initialising the RNG either from u-boot or OPTEE. In this case
> > > u-
> > > boot is
> > >     the right place to-do that because there's upstream code in
> > > u-boot
> > > that
> > >     just works. Patch #2 does that for the WaRP7.
> > > 
> > > 3. Ensuring the job-ring registers are assigned to the non
> > > TrustZone
> > > mode.
> > >     On the i.MX7 after the BootROM runs the job-ring registers
> > > are
> > > assigned
> > >     to TrustZone. Patch #1 does that for all CAAM hardware.
> > > 
> > 
> > I did have the same issue, not with booting OPTEE, but booting
> > Linux in
> > non-secure mode. #2 and #3 are required to handle this problem, but
> > #1
> > is not needed.
> > 
> > The CAAM kernel driver always tries to instantiate all RNG state
> > handles directly using DEC0 (which is only accessible from secure
> > mode). The u-boot driver however only instantiates the first state
> > handle, which is why the kernel driver then goes on and tries to
> > instantiate the second one. This is solved by simply instantiating
> > all
> > RNG state handles in the CAAM u-boot driver.
> > 
> > I can prepare a patch to implement this, if there is interest. This
> > is
> > tested to work with the mainline kernel and I assume that it would
> > work
> > with the NXP kernel as well. Further patches are however needed to
> > support the imx7 in the CAAM kernel driver.
> 
> So I just sent out a patch-set for i.MX7 covering this - I added you
> to 
> the CC list for that.
> 
> The guidance from NXP (and my experience) is that the current kernel 
> driver bugs-out when it can't touch the deco registers.
> 
> I have a bunch of fixes around that.

Thanks for adding me to the CC list.

I have experienced the same thing regarding the dec0 registers.
However, I don't understand why you want to detect secure mode in the
kernel driver to skip RNG instantiation instead of instantiating all
RNG state handles in the u-boot driver. This way, the kernel driver
would skip both state handles (instead of just the first one as with
the current u-boot driver) in the probe call. The dec0 registers would
therefore never be used.

In addition, skipping RNG instantiation in the kernel driver means that
the second state handle never gets instantiated.

> > 
> > > On point #3 this ordinarily isn't a problem because unless
> > > TrustZone
> > > is
> > > activated the restrictions on the job-ring registers don't kick
> > > in,
> > > its
> > > only after enabling TrustZone that Linux will loose access to the
> > > job-ring
> > > registers.
> > > 
> > > Finally should OPTEE or another TEE want to do things with the
> > > job-
> > > ring
> > > registers it will have sufficient privilege to assign whichever
> > > job-
> > > ring
> > > registers it wants to OPTEE/TEE but will naturally then have to
> > > arbitrate
> > > with Linux to inform the Kernel CAAM driver which job-ring
> > > registers
> > > it can
> > > and cannot access.
> > > 
> > > That arbitration process is for a future putative OPTEE/TEE CAAM
> > > driver to
> > > solve and is out of scope of this patchset.
> > 
> > This is actually quite simple to solve, since each job ring has a
> > separate device tree node. Simply disabling all job rings used by
> > OPTEE
> > / secure world software should be sufficient.
> 
> Yes I agree. Then again there is currently no CAAM/OPTEE driver so 
> nothing to-do.