Re: [edk2-devel] [PATCH v2 3/4] OvmfPkg: Enable physical presence interface for TPM 1.2

["Yao, Jiewen" <jiewen.yao@intel.com>]

The PPFlag variable MUST to be locked to prevent malicious modification.
Otherwise, anyone can change the PP configuration without confirmation from end user.

Thank you
Yao Jiewen


> -----Original Message-----
> From: Gerd Hoffmann <kraxel@redhat.com>
> Sent: Monday, November 8, 2021 7:58 PM
> To: Stefan Berger <stefanb@linux.ibm.com>
> Cc: devel@edk2.groups.io; marcandre.lureau@redhat.com; Yao, Jiewen
> <jiewen.yao@intel.com>; Wang, Jian J <jian.j.wang@intel.com>; Ard Biesheuvel
> <ardb+tianocore@kernel.org>; Justen, Jordan L <jordan.l.justen@intel.com>
> Subject: Re: [edk2-devel] [PATCH v2 3/4] OvmfPkg: Enable physical presence
> interface for TPM 1.2
> 
> On Sat, Nov 06, 2021 at 09:19:33PM -0400, Stefan Berger wrote:
> >
> > On 11/5/21 08:17, Gerd Hoffmann wrote:
> > > On Tue, Nov 02, 2021 at 11:49:09AM -0400, Stefan Berger wrote:
> > > > Enable the physical presence interface for TPM 1.2. It is required for the
> > > > TPM 1.2 menu to work.
> > > >
> > > > The changes to DxeTcgPhysicalPresenceLib.c are due to the device we are
> using
> > > > in QEMU for presenting the supported PPI commands and results to the OS
> via
> > > > ACPI as well as to store the PPI opcode to execute.
> > > Fails to build for microvm.
> > >
> > > > +
> TcgPhysicalPresenceLib|OvmfPkg/Library/TcgPhysicalPresenceLibNull/DxeTcgPh
> ysicalPresenceLib.inf
> > > I guess this line is needed just next to Tcg2PhysicalPresenceLibNull
> > > line?
> > > (same problem on OvmfXen.dsc)
> >
> > Fixed in v3 for microvm and Xen and Bhyve also.
> >
> > You happen to know about the variable lock issue? Why does the variable need
> > to be locked?
> 
> No clue, sorry.  That's a topic I have to learn about myself.  Noticed
> the variable locking deprecation warning in the ovmf boot log too, but
> havn't found the time yet to look into that.
> 
> take care,
>   Gerd