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

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

On Wed, Jul 30, 2014 at 04:36:38PM +0200, Laszlo Ersek wrote:
> 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 <stefanb@linux.vnet.ibm.com>
> >>
> >> 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.
> 
> Thanks
> Laszlo

Assuming we want guest to allocate it, I think the way
would be to add a new zone for the linker, e.g. PHYSICAL.
You would then parse only these entries and ignore
others, this way you can still use EFI_ACPI_TABLE_PROTOCOL.