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

[Michael S. Tsirkin]

On Wed, Jul 30, 2014 at 05:37:26PM +0200, Laszlo Ersek wrote:
> On 07/30/14 17:10, 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);
> 
> (Responding wrt. to OVMF:) because EFI_ACPI_TABLE_PROTOCOL special cases
> the installation of FACS. This is visible both in the UEFI
> specification, and in the edk2 implementation.
> 
> That is, OVMF can avoid relocating the "fadt->firmware_ctrl" pointer,
> because edk2's EFI_ACPI_TABLE_PROTOCOL will do that automatically, when
> OVMF requests the installation of FACS.
> 
> No such special case exists for the installation of the TCG event log
> area (which is by itself not even an ACPI table as I gather). *If* the
> TCG event log were an ACPI table in its own right, *and* edk2's
> EFI_ACPI_TABLE_PROTOCOL implementation had a special case for it, then
> when OVMF installed the event log, EFI_ACPI_TABLE_PROTOCOL would update
> TCPA.LASA to it.
> 
> Thanks
> Laszlo

How does EFI want to handle TCPA? Does caller allocate it
log and fill in the address?


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