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+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.