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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/specs/tpm.txt | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/docs/specs/tpm.txt b/docs/specs/tpm.txt index e4bb094..424d151 100644 --- a/docs/specs/tpm.txt +++ b/docs/specs/tpm.txt @@ -76,6 +76,89 @@ URL: https://trustedcomputinggroup.org/tcg-acpi-specification/ +== ACPI PPI Interface == + +QEMU supports the Physical Presence Interface (PPI) for TPM 1.2 and TPM 2. This +interface requires ACPI and firmware support. The specification can be found at +the following URL: + +https://trustedcomputinggroup.org/resource/tcg-physical-presence-interface-specification/ + +PPI enables a system administrator (root) to request a modification to the +TPM upon reboot. The PPI specification defines the operation requests and the +actions the firmware has to take. The system administrator passes the operation +request number to the firmware through an ACPI interface which writes this +number to a memory location that the firmware knows. Upon reboot, the firmware +finds the number and sends commands to the the TPM. The firmware writes the TPM +result code and the operation request number to a memory location that ACPI can +read from and pass the result on to the administrator. + +The PPI specification defines a set of mandatory and optional operations for +the firmware to implement. The ACPI interface also allows an administrator to +list the supported operations. In QEMU the ACPI code is generated by QEMU, yet +the firmware needs to implement support on a per-operations basis, and +different firmwares may support a different subset. Therefore, QEMU introduces +the virtual memory device for PPI where the firmware can indicate which +operations it supports and ACPI can enable the ones that are supported and +disable all others. This interface lies in main memory and has the following +layout: + + +----------+--------+--------+-------------------------------------------+ + | Field | Length | Offset | Description | + +----------+--------+--------+-------------------------------------------+ + | func | 0x100 | 0x000 | Firmware sets values for each supported | + | | | | operation. See defined values below. | + +----------+--------+--------+-------------------------------------------+ + | ppin | 0x1 | 0x100 | SMI interrupt to use. Set by firmware. | + | | | | Not supported. | + +----------+--------+--------+-------------------------------------------+ + | ppip | 0x4 | 0x101 | ACPI function index to pass to SMM code. | + | | | | Set by ACPI. Not supported. | + +----------+--------+--------+-------------------------------------------+ + | pprp | 0x4 | 0x105 | Result of last executed operation. Set by | + | | | | firmware. See function index 5 for values.| + +----------+--------+--------+-------------------------------------------+ + | pprq | 0x4 | 0x109 | Operation request number to execute. See | + | | | | 'Physical Presence Interface Operation | + | | | | Summary' tables in specs. Set by ACPI. | + +----------+--------+--------+-------------------------------------------+ + | pprm | 0x4 | 0x10d | Operation request optional parameter. | + | | | | Values depend on operation. Set by ACPI. | + +----------+--------+--------+-------------------------------------------+ + | lppr | 0x4 | 0x111 | Last executed operation request number. | + | | | | Copied from pprq field by firmware. | + +----------+--------+--------+-------------------------------------------+ + | fret | 0x4 | 0x115 | Result code from SMM function. | + | | | | Not supported. | + +----------+--------+--------+-------------------------------------------+ + | res1 | 0x40 | 0x119 | Reserved for future use | + +----------+--------+--------+-------------------------------------------+ + | next_step| 0x1 | 0x159 | Operation to execute after reboot by | + | | | | firmware. Used by firmware. | + +----------+--------+--------+-------------------------------------------+ + + The following values are supported for the 'func' field. They correspond + to the values used by ACPI function index 8. + + +----------+-------------------------------------------------------------+ + | value | Description | + +----------+-------------------------------------------------------------+ + | 0 | Operation is not implemented. | + +----------+-------------------------------------------------------------+ + | 1 | Operation is only accessible through firmware. | + +----------+-------------------------------------------------------------+ + | 2 | Operation is blocked for OS by firmware configuration. | + +----------+-------------------------------------------------------------+ + | 3 | Operation is allowed and physically present user required. | + +----------+-------------------------------------------------------------+ + | 4 | Operation is allowed and physically present user is not | + | | required. | + +----------+-------------------------------------------------------------+ + +The location of the table is given by the fw_cfg tpmppi_address field. +The PPI memory region size is 0x400 (TPM_PPI_ADDR_SIZE) to leave +enough room for future updates. + QEMU files related to TPM ACPI tables: - hw/i386/acpi-build.c |