Re: RFC: ProtocolLib for cross DXE and SMM Protocol and Handle Services

["Kinney, Michael D" <michael.d.kinney@intel.com>]

Eugene,

I agree that accessing DXE protocols in an SMI handler is not allowed.

It is legal for an SMM Driver to access DXE content in the SMM Driver Entry Point.

For example, if an SMM Driver depends on PCDs, the PCD values can be read from the 
PCD database through the PCD Protocol in the driver entry point.

If you are providing an abstraction for policy data, would a PCD be a better way 
to store/access that information that already works for all phases?

Thanks,

Mike

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Cohen, Eugene
> Sent: Monday, October 10, 2016 1:11 PM
> To: Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming
> <liming.gao@intel.com>; Laszlo Ersek <lersek@redhat.com>; edk2-devel@lists.01.org
> <edk2-devel@ml01.01.org>; Yao, Jiewen <jiewen.yao@intel.com>; Andrew Fish
> (afish@apple.com) <afish@apple.com>
> Subject: Re: [edk2] RFC: ProtocolLib for cross DXE and SMM Protocol and Handle
> Services
> 
> Mike,
> 
> > Can you provide examples in EDK II today where the same GUID Value
> > and Structure definition
> > are used in both the UEFI Handle Database and the SMM Handle
> > Database.
> 
> The example exists in our internal code right now.  We have two platform families:
> one with SMM and one without.  We have a library, originally developed as a DXE
> library, that use a protocol to determine a secure boot policy setting.  This library
> is linked against our variable driver.  In our non-SMM system the variable driver
> runs as a Runtime DXE component and the policy protocol referenced is published in
> the Boot Services protocol DB.  In our SMM system the variable driver runs in SMM and
> the policy protocol is published in the SMM protocol DB.  The protocol is identical
> and uses the same GUID.  So in this scenario we don't install the protocol
> simultaneously in both environments, rather we have different platforms where the
> protocol resides on one side or the other.  Since this protocol is really simple
> (it's not using events, TPL or depending on UEFI boot services stuff) it works well
> for this model.
> 
> > I am aware of cases where an SMM Driver looks for protocols in the
> > DXE Handle database,
> > but I don't think your proposed lib would cover that case.
> 
> Correct - in our usage we are trying to discourage the cross-pollination of SMM and
> DXE in this way since security minded people get nervous when SMM executes outside of
> the secure sandbox.
> 
> Thanks,
> 
> Eugene
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