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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. |