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

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

On Wed, Jul 30, 2014 at 06:07:28PM +0200, Laszlo Ersek wrote:
> On 07/30/14 17:52, Michael S. Tsirkin wrote:
> > On Wed, Jul 30, 2014 at 05:37:26PM +0200, Laszlo Ersek wrote:
> >> On 07/30/14 17:10, Stefan Berger wrote:
> >>> Laszlo Ersek <lersek@redhat.com> wrote on 07/30/2014 10:36:38 AM:
> >>>
> >>>> From: Laszlo Ersek <lersek@redhat.com>
> >>>> To: "Michael S. Tsirkin" <mst@redhat.com>, Stefan Berger/Watson/IBM@IBMUS
> >>>> Cc: qemu-devel@nongnu.org, Stefan Berger <stefanb@linux.vnet.ibm.com>
> >>>> 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 <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.
> >>>
> >>> 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?
> 
> TPM 1.2 seems to be completely absent from edk2, so I have no clue. TPM
> 2.0 appears to be supported, but I already grepped edk2 for how it
> handles the related ACPI table(s), and it doesn't. As far as I can see.

So it will basically just add it to RSDT and assume log pointer is
filled in correctly by caller?

> In the long term, if you can find a way to make it work with SeaBIOS,
> inside the linker/loader framework, that should work under OVMF as well.
> I hope. Famous last words.
> 
> Laszlo