Re: [PATCH edk2-platforms 6/7] Platform/DeveloperBox: add .DSC/.FDF description of MM components

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Thu, 17 Jan 2019 at 13:18, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>
> On Thu, 17 Jan 2019 at 13:08, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> >
> > On Thu, Jan 17, 2019 at 12:10:01PM +0100, Ard Biesheuvel wrote:
> > > > >  ################################################################################
> > > > >  #
> > > > > @@ -294,8 +295,10 @@ [PcdsFixedAtBuild.common]
> > > > >  !endif
> > > > >    gEfiMdeModulePkgTokenSpaceGuid.PcdFirmwareRevision|$(BUILD_NUMBER)
> > > > >
> > > > > -  gArmTokenSpaceGuid.PcdMmBufferBase|0xFFC00000
> > > > > -  gArmTokenSpaceGuid.PcdMmBufferSize|0x00200000
> > > > > +  gEfiSecurityPkgTokenSpaceGuid.PcdUserPhysicalPresence|TRUE
> > > >
> > > > So, I can see why you add this hard-wired for the purpose of testing.
> > > > But please, add a *very* conspicuous, and strongly worded, comment
> > > > statement preceding it.
> > >
> > > Well, I was talking to Peter about this the other day: according to
> > > the spec, this setting should only matter before exit boot services,
> > > and since this platform only supports serial and GOP consoles, one
> > > could argue that only a physically present user could interact with it
> > > before that time.
> >
> > But that also makes the Pcd pointless.
> >
> > > The obvious way of implementing this non-trivially on this platform is
> > > to use a DIP switch, but that requires you to open the case to
> > > enroll/delete the platform key. Perhaps that does not matter, and it
> > > would in fact produce a less dangerous reference implementation.
> >
> > I would be totally OK with that.
> > I would also be totally OK with a DynamicPcd settable through the UI
> > (which is what most machines I come across have).
> >
>
> That won't work for this implementation: the state of dynamic PCDs
> does not propagate into the MM world (nor should it), and so no MM
> driver implementing the dynamic PCD protocol exists.
>
> > But I would also be cool with a sufficiently evil "here be dragons"
> > statement, pointing out that we don't care that much
> > *on*this*specific*system* because the NOR isn't actually hw protected
> > anyway, and this implementation is all about exercising the software
> > stack..
> >
>
> I'll go with that for the time being.

I'll add the following:

diff --git a/Platform/Socionext/DeveloperBox/DeveloperBox.dsc.inc
b/Platform/Socionext/DeveloperBox/DeveloperBox.dsc.inc
index f191edcb78dd..1ac8c8f95722 100644
--- a/Platform/Socionext/DeveloperBox/DeveloperBox.dsc.inc
+++ b/Platform/Socionext/DeveloperBox/DeveloperBox.dsc.inc
@@ -301,6 +301,13 @@
 !endif
   gEfiMdeModulePkgTokenSpaceGuid.PcdFirmwareRevision|$(BUILD_NUMBER)

+  #
+  # NOTE: this platform is not fully secure (the NOR flash is mapped
non-secure)
+  # and so the MM based secure boot implementation it provides should
be treated
+  # as a reference only. For this reason, it does not make a lot of sense to
+  # implement an elaborate PlatformSecureLib implementation that can assert
+  # physical presence, and instead, we'll stick with the default PCD based one.
+  #
   gEfiSecurityPkgTokenSpaceGuid.PcdUserPhysicalPresence|TRUE

   gEfiMdeModulePkgTokenSpaceGuid.PcdMaxVariableSize|0x2000