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diff --git a/docs/specs/tpm.rst b/docs/specs/tpm.rst new file mode 100644 index 0000000000..2bdf637f55 --- /dev/null +++ b/docs/specs/tpm.rst @@ -0,0 +1,503 @@ +=============== +QEMU TPM Device +=============== + +Guest-side hardware interface +============================= + +TIS interface +------------- + +The QEMU TPM emulation implements a TPM TIS hardware interface +following the Trusted Computing Group's specification "TCG PC Client +Specific TPM Interface Specification (TIS)", Specification Version +1.3, 21 March 2013. (see the `TIS specification`_, or a later version +of it). + +The TIS interface makes a memory mapped IO region in the area +0xfed40000-0xfed44fff available to the guest operating system. + +QEMU files related to TPM TIS interface: + - ``hw/tpm/tpm_tis.c`` + - ``hw/tpm/tpm_tis.h`` + +CRB interface +------------- + +QEMU also implements a TPM CRB interface following the Trusted +Computing Group's specification "TCG PC Client Platform TPM Profile +(PTP) Specification", Family "2.0", Level 00 Revision 01.03 v22, May +22, 2017. (see the `CRB specification`_, or a later version of it) + +The CRB interface makes a memory mapped IO region in the area +0xfed40000-0xfed40fff (1 locality) available to the guest +operating system. + +QEMU files related to TPM CRB interface: + - ``hw/tpm/tpm_crb.c`` + +SPAPR interface +--------------- + +pSeries (ppc64) machines offer a tpm-spapr device model. + +QEMU files related to the SPAPR interface: + - ``hw/tpm/tpm_spapr.c`` + +fw_cfg interface +================ + +The bios/firmware may read the ``"etc/tpm/config"`` fw_cfg entry for +configuring the guest appropriately. + +The entry of 6 bytes has the following content, in little-endian: + +.. code-block:: c + + #define TPM_VERSION_UNSPEC 0 + #define TPM_VERSION_1_2 1 + #define TPM_VERSION_2_0 2 + + #define TPM_PPI_VERSION_NONE 0 + #define TPM_PPI_VERSION_1_30 1 + + struct FwCfgTPMConfig { + uint32_t tpmppi_address; /* PPI memory location */ + uint8_t tpm_version; /* TPM version */ + uint8_t tpmppi_version; /* PPI version */ + }; + +ACPI interface +============== + +The TPM device is defined with ACPI ID "PNP0C31". QEMU builds a SSDT +and passes it into the guest through the fw_cfg device. The device +description contains the base address of the TIS interface 0xfed40000 +and the size of the MMIO area (0x5000). In case a TPM2 is used by +QEMU, a TPM2 ACPI table is also provided. The device is described to +be used in polling mode rather than interrupt mode primarily because +no unused IRQ could be found. + +To support measurement logs to be written by the firmware, +e.g. SeaBIOS, a TCPA table is implemented. This table provides a 64kb +buffer where the firmware can write its log into. For TPM 2 only a +more recent version of the TPM2 table provides support for +measurements logs and a TCPA table does not need to be created. + +The TCPA and TPM2 ACPI tables follow the Trusted Computing Group +specification "TCG ACPI Specification" Family "1.2" and "2.0", Level +00 Revision 00.37. (see the `ACPI specification`_, or a later version +of it) + +ACPI PPI Interface +------------------ + +QEMU supports the Physical Presence Interface (PPI) for TPM 1.2 and +TPM 2. This interface requires ACPI and firmware support. (see the +`PPI 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 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. | + +-------------+--------+--------+-------------------------------------------+ + | ``movv`` | 0x1 | 0x15a | Memory overwrite variable | + +-------------+--------+--------+-------------------------------------------+ + +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`` + - ``include/hw/acpi/tpm.h`` + +TPM backend devices +=================== + +The TPM implementation is split into two parts, frontend and +backend. The frontend part is the hardware interface, such as the TPM +TIS interface described earlier, and the other part is the TPM backend +interface. The backend interfaces implement the interaction with a TPM +device, which may be a physical or an emulated device. The split +between the front- and backend devices allows a frontend to be +connected with any available backend. This enables the TIS interface +to be used with the passthrough backend or the swtpm backend. + +QEMU files related to TPM backends: + - ``backends/tpm.c`` + - ``include/sysemu/tpm_backend.h`` + - ``include/sysemu/tpm_backend_int.h`` + +The QEMU TPM passthrough device +------------------------------- + +In case QEMU is run on Linux as the host operating system it is +possible to make the hardware TPM device available to a single QEMU +guest. In this case the user must make sure that no other program is +using the device, e.g., /dev/tpm0, before trying to start QEMU with +it. + +The passthrough driver uses the host's TPM device for sending TPM +commands and receiving responses from. Besides that it accesses the +TPM device's sysfs entry for support of command cancellation. Since +none of the state of a hardware TPM can be migrated between hosts, +virtual machine migration is disabled when the TPM passthrough driver +is used. + +Since the host's TPM device will already be initialized by the host's +firmware, certain commands, e.g. ``TPM_Startup()``, sent by the +virtual firmware for device initialization, will fail. In this case +the firmware should not use the TPM. + +Sharing the device with the host is generally not a recommended usage +scenario for a TPM device. The primary reason for this is that two +operating systems can then access the device's single set of +resources, such as platform configuration registers +(PCRs). Applications or kernel security subsystems, such as the Linux +Integrity Measurement Architecture (IMA), are not expecting to share +PCRs. + +QEMU files related to the TPM passthrough device: + - ``hw/tpm/tpm_passthrough.c`` + - ``hw/tpm/tpm_util.c`` + - ``hw/tpm/tpm_util.h`` + + +Command line to start QEMU with the TPM passthrough device using the host's +hardware TPM ``/dev/tpm0``: + +.. code-block:: console + + qemu-system-x86_64 -display sdl -accel kvm \ + -m 1024 -boot d -bios bios-256k.bin -boot menu=on \ + -tpmdev passthrough,id=tpm0,path=/dev/tpm0 \ + -device tpm-tis,tpmdev=tpm0 test.img + + +The following commands should result in similar output inside the VM +with a Linux kernel that either has the TPM TIS driver built-in or +available as a module: + +.. code-block:: console + + # dmesg | grep -i tpm + [ 0.711310] tpm_tis 00:06: 1.2 TPM (device=id 0x1, rev-id 1) + + # dmesg | grep TCPA + [ 0.000000] ACPI: TCPA 0x0000000003FFD191C 000032 (v02 BOCHS \ + BXPCTCPA 0000001 BXPC 00000001) + + # ls -l /dev/tpm* + crw-------. 1 root root 10, 224 Jul 11 10:11 /dev/tpm0 + + # find /sys/devices/ | grep pcrs$ | xargs cat + PCR-00: 35 4E 3B CE 23 9F 38 59 ... + ... + PCR-23: 00 00 00 00 00 00 00 00 ... + +The QEMU TPM emulator device +---------------------------- + +The TPM emulator device uses an external TPM emulator called 'swtpm' +for sending TPM commands to and receiving responses from. The swtpm +program must have been started before trying to access it through the +TPM emulator with QEMU. + +The TPM emulator implements a command channel for transferring TPM +commands and responses as well as a control channel over which control +commands can be sent. (see the `SWTPM protocol`_ specification) + +The control channel serves the purpose of resetting, initializing, and +migrating the TPM state, among other things. + +The swtpm program behaves like a hardware TPM and therefore needs to +be initialized by the firmware running inside the QEMU virtual +machine. One necessary step for initializing the device is to send +the TPM_Startup command to it. SeaBIOS, for example, has been +instrumented to initialize a TPM 1.2 or TPM 2 device using this +command. + +QEMU files related to the TPM emulator device: + - ``hw/tpm/tpm_emulator.c`` + - ``hw/tpm/tpm_util.c`` + - ``hw/tpm/tpm_util.h`` + +The following commands start the swtpm with a UnixIO control channel over +a socket interface. They do not need to be run as root. + +.. code-block:: console + + mkdir /tmp/mytpm1 + swtpm socket --tpmstate dir=/tmp/mytpm1 \ + --ctrl type=unixio,path=/tmp/mytpm1/swtpm-sock \ + --log level=20 + +Command line to start QEMU with the TPM emulator device communicating +with the swtpm (x86): + +.. code-block:: console + + qemu-system-x86_64 -display sdl -accel kvm \ + -m 1024 -boot d -bios bios-256k.bin -boot menu=on \ + -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \ + -tpmdev emulator,id=tpm0,chardev=chrtpm \ + -device tpm-tis,tpmdev=tpm0 test.img + +In case a pSeries machine is emulated, use the following command line: + +.. code-block:: console + + qemu-system-ppc64 -display sdl -machine pseries,accel=kvm \ + -m 1024 -bios slof.bin -boot menu=on \ + -nodefaults -device VGA -device pci-ohci -device usb-kbd \ + -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \ + -tpmdev emulator,id=tpm0,chardev=chrtpm \ + -device tpm-spapr,tpmdev=tpm0 \ + -device spapr-vscsi,id=scsi0,reg=0x00002000 \ + -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x3,drive=drive-virtio-disk0,id=virtio-disk0 \ + -drive file=test.img,format=raw,if=none,id=drive-virtio-disk0 + +In case SeaBIOS is used as firmware, it should show the TPM menu item +after entering the menu with 'ESC'. + +.. code-block:: console + + Select boot device: + 1. DVD/CD [ata1-0: QEMU DVD-ROM ATAPI-4 DVD/CD] + [...] + 5. Legacy option rom + + t. TPM Configuration + +The following commands should result in similar output inside the VM +with a Linux kernel that either has the TPM TIS driver built-in or +available as a module: + +.. code-block:: console + + # dmesg | grep -i tpm + [ 0.711310] tpm_tis 00:06: 1.2 TPM (device=id 0x1, rev-id 1) + + # dmesg | grep TCPA + [ 0.000000] ACPI: TCPA 0x0000000003FFD191C 000032 (v02 BOCHS \ + BXPCTCPA 0000001 BXPC 00000001) + + # ls -l /dev/tpm* + crw-------. 1 root root 10, 224 Jul 11 10:11 /dev/tpm0 + + # find /sys/devices/ | grep pcrs$ | xargs cat + PCR-00: 35 4E 3B CE 23 9F 38 59 ... + ... + PCR-23: 00 00 00 00 00 00 00 00 ... + +Migration with the TPM emulator +=============================== + +The TPM emulator supports the following types of virtual machine +migration: + +- VM save / restore (migration into a file) +- Network migration +- Snapshotting (migration into storage like QoW2 or QED) + +The following command sequences can be used to test VM save / restore. + +In a 1st terminal start an instance of a swtpm using the following command: + +.. code-block:: console + + mkdir /tmp/mytpm1 + swtpm socket --tpmstate dir=/tmp/mytpm1 \ + --ctrl type=unixio,path=/tmp/mytpm1/swtpm-sock \ + --log level=20 --tpm2 + +In a 2nd terminal start the VM: + +.. code-block:: console + + qemu-system-x86_64 -display sdl -accel kvm \ + -m 1024 -boot d -bios bios-256k.bin -boot menu=on \ + -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \ + -tpmdev emulator,id=tpm0,chardev=chrtpm \ + -device tpm-tis,tpmdev=tpm0 \ + -monitor stdio \ + test.img + +Verify that the attached TPM is working as expected using applications +inside the VM. + +To store the state of the VM use the following command in the QEMU +monitor in the 2nd terminal: + +.. code-block:: console + + (qemu) migrate "exec:cat > testvm.bin" + (qemu) quit + +At this point a file called ``testvm.bin`` should exists and the swtpm +and QEMU processes should have ended. + +To test 'VM restore' you have to start the swtpm with the same +parameters as before. If previously a TPM 2 [--tpm2] was saved, --tpm2 +must now be passed again on the command line. + +In the 1st terminal restart the swtpm with the same command line as +before: + +.. code-block:: console + + swtpm socket --tpmstate dir=/tmp/mytpm1 \ + --ctrl type=unixio,path=/tmp/mytpm1/swtpm-sock \ + --log level=20 --tpm2 + +In the 2nd terminal restore the state of the VM using the additional +'-incoming' option. + +.. code-block:: console + + qemu-system-x86_64 -display sdl -accel kvm \ + -m 1024 -boot d -bios bios-256k.bin -boot menu=on \ + -chardev socket,id=chrtpm,path=/tmp/mytpm1/swtpm-sock \ + -tpmdev emulator,id=tpm0,chardev=chrtpm \ + -device tpm-tis,tpmdev=tpm0 \ + -incoming "exec:cat < testvm.bin" \ + test.img + +Troubleshooting migration +------------------------- + +There are several reasons why migration may fail. In case of problems, +please ensure that the command lines adhere to the following rules +and, if possible, that identical versions of QEMU and swtpm are used +at all times. + +VM save and restore: + + - QEMU command line parameters should be identical apart from the + '-incoming' option on VM restore + + - swtpm command line parameters should be identical + +VM migration to 'localhost': + + - QEMU command line parameters should be identical apart from the + '-incoming' option on the destination side + + - swtpm command line parameters should point to two different + directories on the source and destination swtpm (--tpmstate dir=...) + (especially if different versions of libtpms were to be used on the + same machine). + +VM migration across the network: + + - QEMU command line parameters should be identical apart from the + '-incoming' option on the destination side + + - swtpm command line parameters should be identical + +VM Snapshotting: + - QEMU command line parameters should be identical + + - swtpm command line parameters should be identical + + +Besides that, migration failure reasons on the swtpm level may include +the following: + + - the versions of the swtpm on the source and destination sides are + incompatible + + - downgrading of TPM state may not be supported + + - the source and destination libtpms were compiled with different + compile-time options and the destination side refuses to accept the + state + + - different migration keys are used on the source and destination side + and the destination side cannot decrypt the migrated state + (swtpm ... --migration-key ... ) + + +.. _TIS specification: + https://trustedcomputinggroup.org/pc-client-work-group-pc-client-specific-tpm-interface-specification-tis/ + +.. _CRB specification: + https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ + + +.. _ACPI specification: + https://trustedcomputinggroup.org/tcg-acpi-specification/ + +.. _PPI specification: + https://trustedcomputinggroup.org/resource/tcg-physical-presence-interface-specification/ + +.. _SWTPM protocol: + https://github.com/stefanberger/swtpm/blob/master/man/man3/swtpm_ioctls.pod |