Re: [Qemu-devel] [PATCH v3 4/4] tpm: add a fake ACPI memory clear interface

["Marc-André Lureau" <marcandre.lureau@gmail.com>]

On Thu, Jun 21, 2018 at 4:33 PM, Igor Mammedov <imammedo@redhat.com> wrote:
> On Thu, 21 Jun 2018 15:24:44 +0200
> Marc-André Lureau <marcandre.lureau@gmail.com> wrote:
>
>> Hi
>>
>> On Thu, Jun 21, 2018 at 3:02 PM, Igor Mammedov <imammedo@redhat.com> wrote:
>> > On Tue, 15 May 2018 14:14:33 +0200
>> > Marc-André Lureau <marcandre.lureau@redhat.com> wrote:
>> >
>> >> This allows to pass the last failing test from the Windows HLK TPM 2.0
>> >> TCG PPI 1.3 tests.
>> >>
>> >> The interface is described in the "TCG Platform Reset Attack
>> >> Mitigation Specification", chapter 6 "ACPI _DSM Function". Whether or
>> >> not we should have a real implementation remains an open question to me.
>> > might it cause security issues?
>>
>> Good question. If the guest assumes success of this operation perhaps.
>> I'll check the spec.
>>
>> > What are implications of faking it and how hard it's to implement thing
>> > per spec?
>>
>> Laszlo answerd that in "[Qemu-devel] investigating TPM for
>> OVMF-on-QEMU"  2f2b) TCG Memory Clear Interface
> I get that it's optional, but we probably shouldn't advertise/fake
> feature if it's not supported.

As said in the commit message, the objective was to pass the Windows
HLK test. If we don't want to advertize a fake interface, I am fine
droping this patch. We'll have to revisit with Laszlo the work needed
in the firmware to support it.

>
>>
>> >
>> >
>> >> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>> >> ---
>> >>  hw/i386/acpi-build.c | 9 +++++++++
>> >>  1 file changed, 9 insertions(+)
>> >>
>> >> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
>> >> index 95be4f0710..392a1e50bd 100644
>> >> --- a/hw/i386/acpi-build.c
>> >> +++ b/hw/i386/acpi-build.c
>> >> @@ -2072,6 +2072,15 @@ build_tpm_ppi(Aml *dev)
>> >>              aml_append(ifctx, aml_return(aml_buffer(1, zerobyte)));
>> >>          }
>> >>          aml_append(method, ifctx);
>> >> +
>> >> +       /* dummy MOR Memory Clear for the sake of WLK PPI test */
>> >> +        ifctx = aml_if(
>> >> +            aml_equal(aml_arg(0),
>> >> +                      aml_touuid("376054ED-CC13-4675-901C-4756D7F2D45D")));
>> >> +        {
>> >> +            aml_append(ifctx, aml_return(aml_int(0)));
>> >> +        }
>> >> +        aml_append(method, ifctx);
>> >>      }
>> >>      aml_append(dev, method);
>> >>  }
>> >
>> >
>>
>>
>>
>



-- 
Marc-André Lureau