Re: [Qemu-devel] [PATCH v2] Add ACPI tables for TPM

[Stefan Berger]

Laszlo Ersek <address@hidden> wrote on 07/30/2014
11:41:10 AM:

> From: Laszlo Ersek <address@hidden>
> To: Stefan Berger/Watson/address@hidden, "Michael
S. Tsirkin" <address@hidden>
> Cc: address@hidden, Stefan Berger <address@hidden>
> Date: 07/30/2014 11:41 AM
> Subject: Re: [PATCH v2] Add ACPI tables for TPM
> 
> On 07/30/14 17:29, Stefan Berger wrote:
> > "Michael S. Tsirkin" <address@hidden> wrote on
07/30/2014 11:20:41 AM:
> > 
> >> From: "Michael S. Tsirkin" <address@hidden>
> >> To: Stefan Berger/Watson/address@hidden
> >> Cc: Laszlo Ersek <address@hidden>, address@hidden,
Stefan
> >> Berger <address@hidden>
> >> Date: 07/30/2014 11:20 AM
> >> Subject: Re: [PATCH v2] Add ACPI tables for TPM
> >>
> >> On Wed, Jul 30, 2014 at 11:10:27AM -0400, Stefan Berger wrote:
> >> > Laszlo Ersek <address@hidden> wrote on 07/30/2014
10:36:38 AM:
> >> >
> >> > > From: Laszlo Ersek <address@hidden>
> >> > > To: "Michael S. Tsirkin" <address@hidden>,
Stefan
> > Berger/Watson/address@hidden
> >> > > Cc: address@hidden, Stefan Berger <address@hidden>
> >> > > Date: 07/30/2014 10:36 AM
> >> > > Subject: Re: [PATCH v2] Add ACPI tables for TPM
> >> > >
> >> > > On 07/30/14 15:20, Michael S. Tsirkin wrote:
> >> > > > On Tue, Jul 29, 2014 at 06:52:19AM -0400,
Stefan Berger wrote:
> >> > > >> From: Stefan Berger <address@hidden>
> >> > > >>
> >> > > >> Add an SSDT ACPI table for the TPM device.
> >> > > >> Add a TCPA table for BIOS logging area
when a TPM is being used.
> >> > > >>
> >> > > >> The latter follows this spec here:
> >> > > >>
> >> > > >> http://www.trustedcomputinggroup.org/files/static_page_files/
> >> > > DCD4188E-1A4B-B294-D050A155FB6F7385/
> >> > > TCG_ACPIGeneralSpecification_PublicReview.pdf
> >> > >
> >> > > (Thanks for CC'ing me, Michael.)
> >> > >
> >> > > I skimmed this spec.
> >> > >
> >> > > >> +static void
> >> > > >> +build_tpm_tcpa(GArray *table_data, GArray
*linker)
> >> > > >> +{
> >> > > >> +    Acpi20Tcpa *tcpa;
> >> > > >> +    uint32_t log_area_minimum_length
= TPM_LOG_AREA_MINIMUM_SIZE;
> >> > > >> +    uint64_t log_area_start_address;
> >> > > >> +    size_t len = log_area_minimum_length
+ sizeof(*tcpa);
> >> > > >> +
> >> > > >> +    log_area_start_address
= table_data->len + sizeof(*tcpa);
> >> > > >> +
> >> > > >> +    tcpa = acpi_data_push(table_data,
len);
> >> > > >> +
> >> > > >> +    tcpa->platform_class
=
> > cpu_to_le16(TPM_TCPA_ACPI_CLASS_CLIENT);
> >> > > >> +    tcpa->log_area_minimum_length
= cpu_to_le32
> >> (log_area_minimum_length);
> >> > > >> +    tcpa->log_area_start_address
= cpu_to_le64
> >> (log_area_start_address);
> >> > > >> +
> >> > > >> +    /* LASA address to be filled
by Guest linker */
> >> > > >
> >> > > > Hmm, you are simply allocating log area as
part of the ACPI
> > table.  It
> >> > > > works because bios happens to allocate tables
from high memory.
> >> > > > But I think this is a problem in practice
because
> >> > > > bios is allowed to allocate acpi memory differently.
> >> > > > On the other hand log presumably needs to
reside in
> >> > > > physical memory somewhere.
> >> > > >
> >> > > > If you need bios to allocate this memory,
then we will
> >> > > > need a new allocation type for this, add it
to linker
> >> > > > in bios and qemu.
> >> > > >
> >> > > > Alternatively, find some other way to get
hold of
> >> > > > physical memory.
> >> > > > Is there a way to disable the log completely?
> >> > > > As defined in your patch, I doubt there's
anything there, ever ..
> >> > > >
> >> > > >
> >> > > >
> >> > > >> +    bios_linker_loader_add_pointer(linker,
ACPI_BUILD_TABLE_FILE,
> >> > > >> +            
                     
ACPI_BUILD_TABLE_FILE,
> >> > > >> +            
                     
table_data,
> >> > > &tcpa->log_area_start_address,
> >> > > >> +            
                     
sizeof
> >> (tcpa->log_area_start_address));
> >> > > >> +    build_header(linker, table_data,
> >> > > >> +            
    (void *)tcpa, "TCPA", sizeof(*tcpa), 2);
> >> > > >> +}
> >> > >
> >> > > So here's my understanding. The spec referenced
above describes three
> >> > > ACPI tables: two (client vs. server) for TPM 1.2,
and a third one
> >> > > (usable by both client & server platforms)
for TPM 2.0.
> >> > >
> >> > > The code above prepares a TPM 1.2 table. (Signature:
"TCPA".)
> >> > >
> >> > > This table has a field called LASA (Log Area Start
Address) which
> > points
> >> > > to somewhere in (guest-)physical memory. The patch
adds a "dummy
> > range"
> >> > > to the end of the TCPA table itself, and asks the
linker to set
> > LASA to
> >> > > the beginning of that range.
> >> > >
> >> > > This won't work in OVMF, and not just because of
the reason that
> > Michael
> >> > > mentions (ie. because the firmware, in particular
SeaBIOS, might
> >> > > allocate the TCPA table in an area that is unsuitable
as LASA target).
> >> > >
> >> > > Rather, in OVMF this won't work because OVMF doesn't
implement the
> >> > > linking part of the linker. The *generic* edk2
protocol
> >> > > (EFI_ACPI_TABLE_PROTOCOL, which is coded outside
of OVMF) that
> > OVMF uses
> >> > > (as a client) to install ACPI tables in guest-phys
memory requires
> >> > > tables to be passed in one-by-one.
> >> > >
> >> > > The EFI_ACPI_TABLE_PROTOCOL implementation in edk2
handles *some*
> >> > > well-known tables specially. It has knowledge of
their internal
> >> > > pointers, and when you install an ACPI table, EFI_ACPI_TABLE_PROTOCOL
> >> > > updates pointers automatically. (For example when
you install the
> > FACS,
> >> > > the protocol links it automatically into FACP.)
> >> > >
> >> > > The EFI_ACPI_TABLE_PROTOCOL implementation in edk2
doesn't seem to
> > know
> >> > > anything about the TCPA table, let alone the unstructured
(?) TCG
> > event
> >> > > log that is pointed-to by TCPA.LASA.
> >> > >
> >> > > (I grepped for the TCPA signature,
> >> > >
> >> >
> >>
> > 
> EFI_ACPI_5_0_TRUSTED_COMPUTING_PLATFORM_ALLIANCE_CAPABILITIES_TABLE_SIGNATURE.)
> >> > >
> >> > > This means that if you pass down a TCPA table,
OVMF will install it
> >> > > right now, but TCPA.LASA will be bogus.
> >> > >
> >> > > If I wanted to implement the complete linker as
Michael envisioned it,
> >> > > then I'd have to avoid edk2's EFI_ACPI_TABLE_PROTOCOL,
and implement
> >> > > ACPI table installation from zero, trying to mimic
the SeaBIOS client
> >> > > code, but in a way that matches the UEFI environment.
I'm not ready to
> >> > > do that. Definitely not without an "official"
human-language
> >> > > specification of the linker-loader interface.
> >> > >
> >> > > I skimmed the patch but I'm not sure what exactly
the TPM emulation in
> >> > > qemu depends on. Is it a command line option? Is
it default for some
> >> > > machine types?
> >> > >
> >> > > Alternatively, I could recognize the TCPA signature
in OVMF when
> > parsing
> >> > > the ACPI blobs for table headers, and filter it
out.
> >> >
> >> > This is the code for what I would call 'pointer relocation'.
The
> >> TCPA table is
> >> > not the only place where this is used, but why is it
an issue
> >> there while not
> >> > with the following?
> >> >
> >> >     fadt->firmware_ctrl = cpu_to_le32(facs);
> >> >     /* FACS address to be filled by Guest
linker */
> >> >     bios_linker_loader_add_pointer(linker,
ACPI_BUILD_TABLE_FILE,  
> >> >                
                   ACPI_BUILD_TABLE_FILE,
> >> >                
                   table_data,
&fadt->firmware_ctrl,
> >> >                
                   sizeof
fadt->firmware_ctrl);
> >> >
> >> > Regards,
> >> >     Stefan
> >>
> >>
> >> Becase FACS is an ACPI table. So BIOS allocates it
> >> from E820_RESERVED at the moment but it does not have to,
> >> it could mark it with E820_ACPI.
> >> Guest can then interpret the tables and then release the
> >> memory if it wishes.
> >>
> >> If you want to do it for TCPA you must tell bios that
> >> this is not ACPI memory.
> > 
> > I see. Presumably the whole slew of FADT, FACS, RSDP, & RSDT
would need
> > a similar tag to keep the S3 resume vector around?
> 
> Not in OVMF, because edk2's EFI_ACPI_TABLE_PROTOCOL special cases
FACS
> (containing the S3 resume vector), allocating it in EfiACPIMemoryNVS
memory.
> 
> Table 26. Memory Type Usage after ExitBootServices()
> EfiACPIMemoryNVS: This memory is to be preserved by the loader and
OS
>                   in
the working and ACPI S1–S3 states.
> 

So what is a solution then for OVMF? Add another special
case for TCPA? Is this counter to the specs ? Skip TCPA?

   Stefan