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Documentation / tpm / xen-tpmfront.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

1	Virtual TPM interface for Xen
2	
3	Authors: Matthew Fioravante (JHUAPL), Daniel De Graaf (NSA)
4	
5	This document describes the virtual Trusted Platform Module (vTPM) subsystem for
6	Xen. The reader is assumed to have familiarity with building and installing Xen,
7	Linux, and a basic understanding of the TPM and vTPM concepts.
8	
9	INTRODUCTION
10	
11	The goal of this work is to provide a TPM functionality to a virtual guest
12	operating system (in Xen terms, a DomU).  This allows programs to interact with
13	a TPM in a virtual system the same way they interact with a TPM on the physical
14	system.  Each guest gets its own unique, emulated, software TPM.  However, each
15	of the vTPM's secrets (Keys, NVRAM, etc) are managed by a vTPM Manager domain,
16	which seals the secrets to the Physical TPM.  If the process of creating each of
17	these domains (manager, vTPM, and guest) is trusted, the vTPM subsystem extends
18	the chain of trust rooted in the hardware TPM to virtual machines in Xen. Each
19	major component of vTPM is implemented as a separate domain, providing secure
20	separation guaranteed by the hypervisor. The vTPM domains are implemented in
21	mini-os to reduce memory and processor overhead.
22	
23	This mini-os vTPM subsystem was built on top of the previous vTPM work done by
24	IBM and Intel corporation.
25	
26	
27	DESIGN OVERVIEW
28	---------------
29	
30	The architecture of vTPM is described below:
31	
32	+------------------+
33	|    Linux DomU    | ...
34	|       |  ^       |
35	|       v  |       |
36	|   xen-tpmfront   |
37	+------------------+
38	        |  ^
39	        v  |
40	+------------------+
41	| mini-os/tpmback  |
42	|       |  ^       |
43	|       v  |       |
44	|  vtpm-stubdom    | ...
45	|       |  ^       |
46	|       v  |       |
47	| mini-os/tpmfront |
48	+------------------+
49	        |  ^
50	        v  |
51	+------------------+
52	| mini-os/tpmback  |
53	|       |  ^       |
54	|       v  |       |
55	| vtpmmgr-stubdom  |
56	|       |  ^       |
57	|       v  |       |
58	| mini-os/tpm_tis  |
59	+------------------+
60	        |  ^
61	        v  |
62	+------------------+
63	|   Hardware TPM   |
64	+------------------+
65	
66	 * Linux DomU: The Linux based guest that wants to use a vTPM. There may be
67		       more than one of these.
68	
69	 * xen-tpmfront.ko: Linux kernel virtual TPM frontend driver. This driver
70	                    provides vTPM access to a Linux-based DomU.
71	
72	 * mini-os/tpmback: Mini-os TPM backend driver. The Linux frontend driver
73			    connects to this backend driver to facilitate communications
74			    between the Linux DomU and its vTPM. This driver is also
75			    used by vtpmmgr-stubdom to communicate with vtpm-stubdom.
76	
77	 * vtpm-stubdom: A mini-os stub domain that implements a vTPM. There is a
78			 one to one mapping between running vtpm-stubdom instances and
79	                 logical vtpms on the system. The vTPM Platform Configuration
80	                 Registers (PCRs) are normally all initialized to zero.
81	
82	 * mini-os/tpmfront: Mini-os TPM frontend driver. The vTPM mini-os domain
83			     vtpm-stubdom uses this driver to communicate with
84			     vtpmmgr-stubdom. This driver is also used in mini-os
85			     domains such as pv-grub that talk to the vTPM domain.
86	
87	 * vtpmmgr-stubdom: A mini-os domain that implements the vTPM manager. There is
88			    only one vTPM manager and it should be running during the
89			    entire lifetime of the machine.  This domain regulates
90			    access to the physical TPM on the system and secures the
91			    persistent state of each vTPM.
92	
93	 * mini-os/tpm_tis: Mini-os TPM version 1.2 TPM Interface Specification (TIS)
94	                    driver. This driver used by vtpmmgr-stubdom to talk directly to
95	                    the hardware TPM. Communication is facilitated by mapping
96	                    hardware memory pages into vtpmmgr-stubdom.
97	
98	 * Hardware TPM: The physical TPM that is soldered onto the motherboard.
99	
100	
101	INTEGRATION WITH XEN
102	--------------------
103	
104	Support for the vTPM driver was added in Xen using the libxl toolstack in Xen
105	4.3.  See the Xen documentation (docs/misc/vtpm.txt) for details on setting up
106	the vTPM and vTPM Manager stub domains.  Once the stub domains are running, a
107	vTPM device is set up in the same manner as a disk or network device in the
108	domain's configuration file.
109	
110	In order to use features such as IMA that require a TPM to be loaded prior to
111	the initrd, the xen-tpmfront driver must be compiled in to the kernel.  If not
112	using such features, the driver can be compiled as a module and will be loaded
113	as usual.
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