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124 lines
4.5 KiB
124 lines
4.5 KiB
============================= |
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Virtual TPM interface for Xen |
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============================= |
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Authors: Matthew Fioravante (JHUAPL), Daniel De Graaf (NSA) |
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This document describes the virtual Trusted Platform Module (vTPM) subsystem for |
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Xen. The reader is assumed to have familiarity with building and installing Xen, |
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Linux, and a basic understanding of the TPM and vTPM concepts. |
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Introduction |
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------------ |
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The goal of this work is to provide a TPM functionality to a virtual guest |
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operating system (in Xen terms, a DomU). This allows programs to interact with |
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a TPM in a virtual system the same way they interact with a TPM on the physical |
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system. Each guest gets its own unique, emulated, software TPM. However, each |
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of the vTPM's secrets (Keys, NVRAM, etc) are managed by a vTPM Manager domain, |
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which seals the secrets to the Physical TPM. If the process of creating each of |
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these domains (manager, vTPM, and guest) is trusted, the vTPM subsystem extends |
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the chain of trust rooted in the hardware TPM to virtual machines in Xen. Each |
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major component of vTPM is implemented as a separate domain, providing secure |
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separation guaranteed by the hypervisor. The vTPM domains are implemented in |
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mini-os to reduce memory and processor overhead. |
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This mini-os vTPM subsystem was built on top of the previous vTPM work done by |
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IBM and Intel corporation. |
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Design Overview |
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--------------- |
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The architecture of vTPM is described below:: |
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+------------------+ |
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| Linux DomU | ... |
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| | ^ | |
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| v | | |
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| xen-tpmfront | |
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+------------------+ |
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| ^ |
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v | |
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+------------------+ |
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| mini-os/tpmback | |
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| | ^ | |
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| v | | |
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| vtpm-stubdom | ... |
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| | ^ | |
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| v | | |
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| mini-os/tpmfront | |
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+------------------+ |
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| ^ |
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v | |
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+------------------+ |
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| mini-os/tpmback | |
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| | ^ | |
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| v | | |
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| vtpmmgr-stubdom | |
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| | ^ | |
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| v | | |
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| mini-os/tpm_tis | |
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+------------------+ |
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| ^ |
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v | |
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+------------------+ |
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| Hardware TPM | |
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+------------------+ |
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* Linux DomU: |
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The Linux based guest that wants to use a vTPM. There may be |
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more than one of these. |
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* xen-tpmfront.ko: |
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Linux kernel virtual TPM frontend driver. This driver |
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provides vTPM access to a Linux-based DomU. |
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* mini-os/tpmback: |
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Mini-os TPM backend driver. The Linux frontend driver |
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connects to this backend driver to facilitate communications |
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between the Linux DomU and its vTPM. This driver is also |
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used by vtpmmgr-stubdom to communicate with vtpm-stubdom. |
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* vtpm-stubdom: |
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A mini-os stub domain that implements a vTPM. There is a |
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one to one mapping between running vtpm-stubdom instances and |
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logical vtpms on the system. The vTPM Platform Configuration |
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Registers (PCRs) are normally all initialized to zero. |
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* mini-os/tpmfront: |
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Mini-os TPM frontend driver. The vTPM mini-os domain |
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vtpm-stubdom uses this driver to communicate with |
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vtpmmgr-stubdom. This driver is also used in mini-os |
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domains such as pv-grub that talk to the vTPM domain. |
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* vtpmmgr-stubdom: |
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A mini-os domain that implements the vTPM manager. There is |
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only one vTPM manager and it should be running during the |
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entire lifetime of the machine. This domain regulates |
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access to the physical TPM on the system and secures the |
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persistent state of each vTPM. |
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* mini-os/tpm_tis: |
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Mini-os TPM version 1.2 TPM Interface Specification (TIS) |
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driver. This driver used by vtpmmgr-stubdom to talk directly to |
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the hardware TPM. Communication is facilitated by mapping |
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hardware memory pages into vtpmmgr-stubdom. |
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* Hardware TPM: |
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The physical TPM that is soldered onto the motherboard. |
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Integration With Xen |
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-------------------- |
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Support for the vTPM driver was added in Xen using the libxl toolstack in Xen |
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4.3. See the Xen documentation (docs/misc/vtpm.txt) for details on setting up |
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the vTPM and vTPM Manager stub domains. Once the stub domains are running, a |
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vTPM device is set up in the same manner as a disk or network device in the |
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domain's configuration file. |
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In order to use features such as IMA that require a TPM to be loaded prior to |
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the initrd, the xen-tpmfront driver must be compiled in to the kernel. If not |
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using such features, the driver can be compiled as a module and will be loaded |
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as usual.
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