Re: [Patch 1/1] MdeModulePkg/Library/VarCheckLib: Allow SetVariable from SMM

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

> -----Original Message-----
> From: Wu, Hao A <hao.a.wu@intel.com>
> Sent: Tuesday, January 5, 2021 9:47 PM
> To: Kinney, Michael D <michael.d.kinney@intel.com>; devel@edk2.groups.io
> Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>; Liming Gao <gaoliming@byosoft.com.cn>
> Subject: RE: [Patch 1/1] MdeModulePkg/Library/VarCheckLib: Allow SetVariable from SMM
> 
> > -----Original Message-----
> > From: Michael D Kinney <michael.d.kinney@intel.com>
> > Sent: Wednesday, January 6, 2021 11:51 AM
> > To: devel@edk2.groups.io
> > Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>; Wu, Hao A
> > <hao.a.wu@intel.com>; Liming Gao <gaoliming@byosoft.com.cn>
> > Subject: [Patch 1/1] MdeModulePkg/Library/VarCheckLib: Allow SetVariable
> > from SMM
> >
> > REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3154
> >
> > Update VarCheckLibSetVariableCheck() to allow locked variables to be
> > updated if the RequestSource is VarCheckFromTrusted even if one or more
> > variable check handlers return EFI_WRITE_PROTECTED.
> > RequestSource is only set to VarCheckFromTrusted if the request is through
> > the EFI_SMM_VARAIBLE_PROTOCOL.
> 
> 
> Hello Mike,
> 
> Sorry for a question.
> 
> If a SetVar request is blocked by a registered VarCheck handler, I think it would better to change that handler to allow
> requests from SMM.
> I am not sure if there is a VarCheck handler that has its own specific rule to return 'EFI_WRITE_PROTECTED' to block some
> SetVar requests.
> Is there any special consideration (e.g. VarCheck handler not being able to get the source of the SetVar request) for not
> doing this way?

The VarCheck handlers do not have the context information.

The VarCheckHandlers function type is the same as EFI_SET_VARIABLE.

    typedef EFI_SET_VARIABLE VAR_CHECK_SET_VARIABLE_CHECK_HANDLER;

EFI_SET_VARIABLE defines EFI_WRITE_PROTECTED return status for
read-only condition.  So using EFI_WRITE_PROTECTED to block a write
for other reasons would not be conformant.

> 
> Thanks in advance.
> 
> Best Regards,
> Hao Wu
> 
> 
> >
> > Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
> > Cc: Hao A Wu <hao.a.wu@intel.com>
> > Cc: Liming Gao <gaoliming@byosoft.com.cn>
> > Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
> > ---
> >  MdeModulePkg/Library/VarCheckLib/VarCheckLib.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/MdeModulePkg/Library/VarCheckLib/VarCheckLib.c
> > b/MdeModulePkg/Library/VarCheckLib/VarCheckLib.c
> > index 470d782444bf..9596d760e945 100644
> > --- a/MdeModulePkg/Library/VarCheckLib/VarCheckLib.c
> > +++ b/MdeModulePkg/Library/VarCheckLib/VarCheckLib.c
> > @@ -1,7 +1,7 @@
> >  /** @file
> >    Implementation functions and structures for var check services.
> >
> > -Copyright (c) 2015 - 2016, Intel Corporation. All rights reserved.<BR>
> > +Copyright (c) 2015 - 2021, Intel Corporation. All rights reserved.<BR>
> >  SPDX-License-Identifier: BSD-2-Clause-Patent
> >
> >  **/
> > @@ -655,6 +655,13 @@ VarCheckLibSetVariableCheck (
> >                 DataSize,
> >                 Data
> >                 );
> > +    if (Status == EFI_WRITE_PROTECTED && RequestSource ==
> > VarCheckFromTrusted) {
> > +      //
> > +      // If RequestSource is trusted, then allow variable to be set even if it
> > +      // is write protected.
> > +      //
> > +      continue;
> > +    }
> >      if (EFI_ERROR (Status)) {
> >        DEBUG ((EFI_D_INFO, "Variable Check handler fail %r - %g:%s\n", Status,
> > VendorGuid, VariableName));
> >        return Status;
> > --
> > 2.29.2.windows.2