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

["Wu, Hao A" <hao.a.wu@intel.com>]

> -----Original Message-----
> From: Kinney, Michael D <michael.d.kinney@intel.com>
> Sent: Thursday, January 7, 2021 12:53 AM
> To: Wu, Hao A <hao.a.wu@intel.com>; devel@edk2.groups.io; Kinney,
> Michael D <michael.d.kinney@intel.com>
> 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: 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.
Reviewed-by: Hao A Wu <hao.a.wu@intel.com>

Best Regards,
Hao Wu


> 
> >
> > 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