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Diffstat (limited to 'Documentation/security/tpm')
| -rw-r--r-- | Documentation/security/tpm/index.rst | 10 | ||||
| -rw-r--r-- | Documentation/security/tpm/tpm_event_log.rst | 55 | ||||
| -rw-r--r-- | Documentation/security/tpm/tpm_ftpm_tee.rst | 27 | ||||
| -rw-r--r-- | Documentation/security/tpm/tpm_vtpm_proxy.rst | 50 | ||||
| -rw-r--r-- | Documentation/security/tpm/xen-tpmfront.rst | 124 |
5 files changed, 266 insertions, 0 deletions
diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst new file mode 100644 index 000000000..fc40e9f23 --- /dev/null +++ b/Documentation/security/tpm/index.rst @@ -0,0 +1,10 @@ +===================================== +Trusted Platform Module documentation +===================================== + +.. toctree:: + + tpm_event_log + tpm_vtpm_proxy + xen-tpmfront + tpm_ftpm_tee diff --git a/Documentation/security/tpm/tpm_event_log.rst b/Documentation/security/tpm/tpm_event_log.rst new file mode 100644 index 000000000..f00f7a1d5 --- /dev/null +++ b/Documentation/security/tpm/tpm_event_log.rst @@ -0,0 +1,55 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +TPM Event Log +============= + +This document briefly describes what TPM log is and how it is handed +over from the preboot firmware to the operating system. + +Introduction +============ + +The preboot firmware maintains an event log that gets new entries every +time something gets hashed by it to any of the PCR registers. The events +are segregated by their type and contain the value of the hashed PCR +register. Typically, the preboot firmware will hash the components to +who execution is to be handed over or actions relevant to the boot +process. + +The main application for this is remote attestation and the reason why +it is useful is nicely put in the very first section of [1]: + +"Attestation is used to provide information about the platform’s state +to a challenger. However, PCR contents are difficult to interpret; +therefore, attestation is typically more useful when the PCR contents +are accompanied by a measurement log. While not trusted on their own, +the measurement log contains a richer set of information than do the PCR +contents. The PCR contents are used to provide the validation of the +measurement log." + +UEFI event log +============== + +UEFI provided event log has a few somewhat weird quirks. + +Before calling ExitBootServices() Linux EFI stub copies the event log to +a custom configuration table defined by the stub itself. Unfortunately, +the events generated by ExitBootServices() don't end up in the table. + +The firmware provides so called final events configuration table to sort +out this issue. Events gets mirrored to this table after the first time +EFI_TCG2_PROTOCOL.GetEventLog() gets called. + +This introduces another problem: nothing guarantees that it is not called +before the Linux EFI stub gets to run. Thus, it needs to calculate and save the +final events table size while the stub is still running to the custom +configuration table so that the TPM driver can later on skip these events when +concatenating two halves of the event log from the custom configuration table +and the final events table. + +References +========== + +- [1] https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/ +- [2] The final concatenation is done in drivers/char/tpm/eventlog/efi.c diff --git a/Documentation/security/tpm/tpm_ftpm_tee.rst b/Documentation/security/tpm/tpm_ftpm_tee.rst new file mode 100644 index 000000000..8c2bae16e --- /dev/null +++ b/Documentation/security/tpm/tpm_ftpm_tee.rst @@ -0,0 +1,27 @@ +============================================= +Firmware TPM Driver +============================================= + +This document describes the firmware Trusted Platform Module (fTPM) +device driver. + +Introduction +============ + +This driver is a shim for firmware implemented in ARM's TrustZone +environment. The driver allows programs to interact with the TPM in the same +way they would interact with a hardware TPM. + +Design +====== + +The driver acts as a thin layer that passes commands to and from a TPM +implemented in firmware. The driver itself doesn't contain much logic and is +used more like a dumb pipe between firmware and kernel/userspace. + +The firmware itself is based on the following paper: +https://www.microsoft.com/en-us/research/wp-content/uploads/2017/06/ftpm1.pdf + +When the driver is loaded it will expose ``/dev/tpmX`` character devices to +userspace which will enable userspace to communicate with the firmware TPM +through this device. diff --git a/Documentation/security/tpm/tpm_vtpm_proxy.rst b/Documentation/security/tpm/tpm_vtpm_proxy.rst new file mode 100644 index 000000000..ea08e76b1 --- /dev/null +++ b/Documentation/security/tpm/tpm_vtpm_proxy.rst @@ -0,0 +1,50 @@ +============================================= +Virtual TPM Proxy Driver for Linux Containers +============================================= + +| Authors: +| Stefan Berger <stefanb@linux.vnet.ibm.com> + +This document describes the virtual Trusted Platform Module (vTPM) +proxy device driver for Linux containers. + +Introduction +============ + +The goal of this work is to provide TPM functionality to each Linux +container. This allows programs to interact with a TPM in a container +the same way they interact with a TPM on the physical system. Each +container gets its own unique, emulated, software TPM. + +Design +====== + +To make an emulated software TPM available to each container, the container +management stack needs to create a device pair consisting of a client TPM +character device ``/dev/tpmX`` (with X=0,1,2...) and a 'server side' file +descriptor. The former is moved into the container by creating a character +device with the appropriate major and minor numbers while the file descriptor +is passed to the TPM emulator. Software inside the container can then send +TPM commands using the character device and the emulator will receive the +commands via the file descriptor and use it for sending back responses. + +To support this, the virtual TPM proxy driver provides a device ``/dev/vtpmx`` +that is used to create device pairs using an ioctl. The ioctl takes as +an input flags for configuring the device. The flags for example indicate +whether TPM 1.2 or TPM 2 functionality is supported by the TPM emulator. +The result of the ioctl are the file descriptor for the 'server side' +as well as the major and minor numbers of the character device that was created. +Besides that the number of the TPM character device is returned. If for +example ``/dev/tpm10`` was created, the number (``dev_num``) 10 is returned. + +Once the device has been created, the driver will immediately try to talk +to the TPM. All commands from the driver can be read from the file descriptor +returned by the ioctl. The commands should be responded to immediately. + +UAPI +==== + +.. kernel-doc:: include/uapi/linux/vtpm_proxy.h + +.. kernel-doc:: drivers/char/tpm/tpm_vtpm_proxy.c + :functions: vtpmx_ioc_new_dev diff --git a/Documentation/security/tpm/xen-tpmfront.rst b/Documentation/security/tpm/xen-tpmfront.rst new file mode 100644 index 000000000..31c67522f --- /dev/null +++ b/Documentation/security/tpm/xen-tpmfront.rst @@ -0,0 +1,124 @@ +============================= +Virtual TPM interface for Xen +============================= + +Authors: Matthew Fioravante (JHUAPL), Daniel De Graaf (NSA) + +This document describes the virtual Trusted Platform Module (vTPM) subsystem for +Xen. The reader is assumed to have familiarity with building and installing Xen, +Linux, and a basic understanding of the TPM and vTPM concepts. + +Introduction +------------ + +The goal of this work is to provide a TPM functionality to a virtual guest +operating system (in Xen terms, a DomU). This allows programs to interact with +a TPM in a virtual system the same way they interact with a TPM on the physical +system. Each guest gets its own unique, emulated, software TPM. However, each +of the vTPM's secrets (Keys, NVRAM, etc) are managed by a vTPM Manager domain, +which seals the secrets to the Physical TPM. If the process of creating each of +these domains (manager, vTPM, and guest) is trusted, the vTPM subsystem extends +the chain of trust rooted in the hardware TPM to virtual machines in Xen. Each +major component of vTPM is implemented as a separate domain, providing secure +separation guaranteed by the hypervisor. The vTPM domains are implemented in +mini-os to reduce memory and processor overhead. + +This mini-os vTPM subsystem was built on top of the previous vTPM work done by +IBM and Intel corporation. + + +Design Overview +--------------- + +The architecture of vTPM is described below:: + + +------------------+ + | Linux DomU | ... + | | ^ | + | v | | + | xen-tpmfront | + +------------------+ + | ^ + v | + +------------------+ + | mini-os/tpmback | + | | ^ | + | v | | + | vtpm-stubdom | ... + | | ^ | + | v | | + | mini-os/tpmfront | + +------------------+ + | ^ + v | + +------------------+ + | mini-os/tpmback | + | | ^ | + | v | | + | vtpmmgr-stubdom | + | | ^ | + | v | | + | mini-os/tpm_tis | + +------------------+ + | ^ + v | + +------------------+ + | Hardware TPM | + +------------------+ + +* Linux DomU: + The Linux based guest that wants to use a vTPM. There may be + more than one of these. + +* xen-tpmfront.ko: + Linux kernel virtual TPM frontend driver. This driver + provides vTPM access to a Linux-based DomU. + +* mini-os/tpmback: + Mini-os TPM backend driver. The Linux frontend driver + connects to this backend driver to facilitate communications + between the Linux DomU and its vTPM. This driver is also + used by vtpmmgr-stubdom to communicate with vtpm-stubdom. + +* vtpm-stubdom: + A mini-os stub domain that implements a vTPM. There is a + one to one mapping between running vtpm-stubdom instances and + logical vtpms on the system. The vTPM Platform Configuration + Registers (PCRs) are normally all initialized to zero. + +* mini-os/tpmfront: + Mini-os TPM frontend driver. The vTPM mini-os domain + vtpm-stubdom uses this driver to communicate with + vtpmmgr-stubdom. This driver is also used in mini-os + domains such as pv-grub that talk to the vTPM domain. + +* vtpmmgr-stubdom: + A mini-os domain that implements the vTPM manager. There is + only one vTPM manager and it should be running during the + entire lifetime of the machine. This domain regulates + access to the physical TPM on the system and secures the + persistent state of each vTPM. + +* mini-os/tpm_tis: + Mini-os TPM version 1.2 TPM Interface Specification (TIS) + driver. This driver used by vtpmmgr-stubdom to talk directly to + the hardware TPM. Communication is facilitated by mapping + hardware memory pages into vtpmmgr-stubdom. + +* Hardware TPM: + The physical TPM that is soldered onto the motherboard. + + +Integration With Xen +-------------------- + +Support for the vTPM driver was added in Xen using the libxl toolstack in Xen +4.3. See the Xen documentation (docs/misc/vtpm.txt) for details on setting up +the vTPM and vTPM Manager stub domains. Once the stub domains are running, a +vTPM device is set up in the same manner as a disk or network device in the +domain's configuration file. + +In order to use features such as IMA that require a TPM to be loaded prior to +the initrd, the xen-tpmfront driver must be compiled in to the kernel. If not +using such features, the driver can be compiled as a module and will be loaded +as usual. |