Re: [Qemu-devel] [PATCH v15 5/6] acpi: add ACPI memory clear interface

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jan 09, 2019 at 06:55:56PM +0400, Marc-André Lureau wrote:
> Hi
> 
> On Wed, Jan 9, 2019 at 6:47 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Wed, Jan 09, 2019 at 12:29:01PM +0400, Marc-André Lureau wrote:
> > > The interface is described in the "TCG Platform Reset Attack
> > > Mitigation Specification", chapter 6 "ACPI _DSM Function". According
> > > to Laszlo, it's not so easy to implement in OVMF, he suggested to do
> > > it in qemu instead.
> > >
> > > See specification documentation for more details, and next commit for
> > > memory clear on reset handling.
> > >
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > >  hw/acpi/tpm.c      | 48 ++++++++++++++++++++++++++++++++++++++++++++++
> > >  docs/specs/tpm.txt |  2 ++
> > >  2 files changed, 50 insertions(+)
> > >
> > > diff --git a/hw/acpi/tpm.c b/hw/acpi/tpm.c
> > > index fee9490306..61da1de97b 100644
> > > --- a/hw/acpi/tpm.c
> > > +++ b/hw/acpi/tpm.c
> > > @@ -53,6 +53,16 @@ void tpm_build_ppi_acpi(TPMIf *tpm, Aml *dev)
> > >      pprq = aml_name("PPRQ");
> > >      pprm = aml_name("PPRM");
> > >
> > > +    aml_append(dev,
> > > +               aml_operation_region(
> > > +                   "TPP3", AML_SYSTEM_MEMORY,
> > > +                   aml_int(TPM_PPI_ADDR_BASE +
> > > +                           0x15a /* movv, docs/specs/tpm.txt */),
> > > +                           0x1
> > > ));
> > > +    field = aml_field("TPP3", AML_BYTE_ACC, AML_NOLOCK, AML_PRESERVE);
> > > +    aml_append(field, aml_named_field("MOVV", 8));
> > > +    aml_append(dev, field);
> > > +
> > >      /*
> > >       * DerefOf in Windows is broken with SYSTEM_MEMORY.  Use a dynamic
> > >       * operation region inside of a method for getting FUNC[op].
> > > @@ -395,6 +405,44 @@ void tpm_build_ppi_acpi(TPMIf *tpm, Aml *dev)
> > >              aml_append(ifctx, aml_return(aml_buffer(1, zerobyte)));
> > >          }
> > >          aml_append(method, ifctx);
> > > +
> > > +        ifctx = aml_if(
> > > +            aml_equal(uuid,
> > > +                      aml_touuid("376054ED-CC13-4675-901C-4756D7F2D45D")));
> > > +        {
> > > +            /* standard DSM query function */
> >
> > refer to spec chapter here?
> 
> Yes, we could add a code comment such as:
> /* "TCG Platform Reset Attack Mitigation Specification", chapter 6
> "ACPI _DSM Function" */

You want to include the version as well.

> 
> >
> > > +            ifctx2 = aml_if(aml_equal(function, zero));
> > > +            {
> > > +                uint8_t byte_list[1] = { 0x03 };
> >
> > and explain 3 above?
> 
> /* functions 1-2 are supported */
> 
> >
> > > +                aml_append(ifctx2, aml_return(aml_buffer(1
> >
> > 1 -> sizeof(byte_list)?
> 
> ok
> 
> >
> > > + , byte_list)));
> > > +            }
> > > +            aml_append(ifctx, ifctx2);
> > > +
> > > +            /*
> > > +             * TCG Platform Reset Attack Mitigation Specification 1.0 Ch.6
> > > +             *
> > > +             * Arg 2 (Integer): Function Index = 1
> > > +             * Arg 3 (Package): Arguments = Package: Type: Integer
> > > +             *                  Operation Value of the Request
> > > +             * Returns: Type: Integer
> > > +             *          0: Success
> > > +             *          1: General Failure
> > > +             */
> > > +            ifctx2 = aml_if(aml_equal(function, one));
> > > +            {
> > > +                aml_append(ifctx2,
> > > +                           aml_store(aml_derefof(aml_index(arguments, zero)),
> > > +                                     op));
> > > +                {
> > > +                    aml_append(ifctx2, aml_store(op, aml_name("MOVV")));
> > > +
> > > +                    /* 0: success */
> > > +                    aml_append(ifctx2, aml_return(zero));
> > > +                }
> > > +            }
> > > +            aml_append(ifctx, ifctx2);
> > > +        }
> > > +        aml_append(method, ifctx);
> > >      }
> > >      aml_append(dev, method);
> > >  }
> > > diff --git a/docs/specs/tpm.txt b/docs/specs/tpm.txt
> > > index 424d1511fc..5d8c26b1ad 100644
> > > --- a/docs/specs/tpm.txt
> > > +++ b/docs/specs/tpm.txt
> > > @@ -135,6 +135,8 @@ layout:
> > >   +----------+--------+--------+-------------------------------------------+
> > >   | next_step|   0x1  |  0x159 | Operation to execute after reboot by      |
> > >   |          |        |        | firmware. Used by firmware.               |
> > > + +----------+--------+--------+-------------------------------------------+
> > > + | movv     |   0x1  |  0x15a | Memory overwrite variable                 |
> > >   +----------+--------+--------+-------------------------------------------+
> > >
> > >     The following values are supported for the 'func' field. They correspond
> > > --
> > > 2.20.1.2.gb21ebb671b
> >
> 
> 
> -- 
> Marc-André Lureau