Stefan Berger | 7e1dc00 | 2016-04-18 13:26:16 -0400 | [diff] [blame] | 1 | Virtual TPM Proxy Driver for Linux Containers |
| 2 | |
| 3 | Authors: Stefan Berger (IBM) |
| 4 | |
| 5 | This document describes the virtual Trusted Platform Module (vTPM) |
| 6 | proxy device driver for Linux containers. |
| 7 | |
| 8 | INTRODUCTION |
| 9 | ------------ |
| 10 | |
| 11 | The goal of this work is to provide TPM functionality to each Linux |
| 12 | container. This allows programs to interact with a TPM in a container |
| 13 | the same way they interact with a TPM on the physical system. Each |
| 14 | container gets its own unique, emulated, software TPM. |
| 15 | |
| 16 | |
| 17 | DESIGN |
| 18 | ------ |
| 19 | |
| 20 | To make an emulated software TPM available to each container, the container |
| 21 | management stack needs to create a device pair consisting of a client TPM |
| 22 | character device /dev/tpmX (with X=0,1,2...) and a 'server side' file |
| 23 | descriptor. The former is moved into the container by creating a character |
| 24 | device with the appropriate major and minor numbers while the file descriptor |
| 25 | is passed to the TPM emulator. Software inside the container can then send |
| 26 | TPM commands using the character device and the emulator will receive the |
| 27 | commands via the file descriptor and use it for sending back responses. |
| 28 | |
| 29 | To support this, the virtual TPM proxy driver provides a device /dev/vtpmx |
| 30 | that is used to create device pairs using an ioctl. The ioctl takes as |
| 31 | an input flags for configuring the device. The flags for example indicate |
| 32 | whether TPM 1.2 or TPM 2 functionality is supported by the TPM emulator. |
| 33 | The result of the ioctl are the file descriptor for the 'server side' |
| 34 | as well as the major and minor numbers of the character device that was created. |
| 35 | Besides that the number of the TPM character device is return. If for |
| 36 | example /dev/tpm10 was created, the number (dev_num) 10 is returned. |
| 37 | |
| 38 | The following is the data structure of the TPM_PROXY_IOC_NEW_DEV ioctl: |
| 39 | |
| 40 | struct vtpm_proxy_new_dev { |
| 41 | __u32 flags; /* input */ |
| 42 | __u32 tpm_num; /* output */ |
| 43 | __u32 fd; /* output */ |
| 44 | __u32 major; /* output */ |
| 45 | __u32 minor; /* output */ |
| 46 | }; |
| 47 | |
| 48 | Note that if unsupported flags are passed to the device driver, the ioctl will |
| 49 | fail and errno will be set to EOPNOTSUPP. Similarly, if an unsupported ioctl is |
| 50 | called on the device driver, the ioctl will fail and errno will be set to |
| 51 | ENOTTY. |
| 52 | |
| 53 | See /usr/include/linux/vtpm_proxy.h for definitions related to the public interface |
| 54 | of this vTPM device driver. |
| 55 | |
| 56 | Once the device has been created, the driver will immediately try to talk |
| 57 | to the TPM. All commands from the driver can be read from the file descriptor |
| 58 | returned by the ioctl. The commands should be responded to immediately. |
| 59 | |
| 60 | Depending on the version of TPM the following commands will be sent by the |
| 61 | driver: |
| 62 | |
| 63 | - TPM 1.2: |
| 64 | - the driver will send a TPM_Startup command to the TPM emulator |
| 65 | - the driver will send commands to read the command durations and |
| 66 | interface timeouts from the TPM emulator |
| 67 | - TPM 2: |
| 68 | - the driver will send a TPM2_Startup command to the TPM emulator |
| 69 | |
| 70 | The TPM device /dev/tpmX will only appear if all of the relevant commands |
| 71 | were responded to properly. |