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+Virtual TPM Proxy Driver for Linux Containers
+
+Authors: Stefan Berger (IBM)
+
+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 return. If for
+example /dev/tpm10 was created, the number (dev_num) 10 is returned.
+
+The following is the data structure of the TPM_PROXY_IOC_NEW_DEV ioctl:
+
+struct vtpm_proxy_new_dev {
+        __u32 flags;         /* input */
+        __u32 tpm_num;       /* output */
+        __u32 fd;            /* output */
+        __u32 major;         /* output */
+        __u32 minor;         /* output */
+};
+
+Note that if unsupported flags are passed to the device driver, the ioctl will
+fail and errno will be set to EOPNOTSUPP. Similarly, if an unsupported ioctl is
+called on the device driver, the ioctl will fail and errno will be set to
+ENOTTY.
+
+See /usr/include/linux/vtpm_proxy.h for definitions related to the public interface
+of this vTPM device driver.
+
+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.
+
+Depending on the version of TPM the following commands will be sent by the
+driver:
+
+- TPM 1.2:
+  - the driver will send a TPM_Startup command to the TPM emulator
+  - the driver will send commands to read the command durations and
+    interface timeouts from the TPM emulator
+- TPM 2:
+  - the driver will send a TPM2_Startup command to the TPM emulator
+
+The TPM device /dev/tpmX will only appear if all of the relevant commands
+were responded to properly.