Re: [PATCH v9 4/4] tpm: Add documentation for the tpm_vtpm device driver

[Jarkko Sakkinen]

On Tue, Mar 29, 2016 at 02:19:14PM -0400, Stefan Berger wrote:
> Add documentation for the tpm_vtpm device driver that implements
> support for providing TPM functionality to Linux containers.
> 
> Parts of this documentation were recycled from the Xen vTPM
> device driver documentation.
> 
> Update the documentation for the ioctl numbers.
> 
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxxxxxxx>
> CC: linux-kernel@xxxxxxxxxxxxxxx
> CC: linux-doc@xxxxxxxxxxxxxxx
> CC: linux-api@xxxxxxxxxxxxxxx

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>

/Jarkko

> ---
>  Documentation/ioctl/ioctl-number.txt |  1 +
>  Documentation/tpm/tpm_vtpm_proxy.txt | 71 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+)
>  create mode 100644 Documentation/tpm/tpm_vtpm_proxy.txt
> 
> diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
> index 91261a3..7dbec90 100644
> --- a/Documentation/ioctl/ioctl-number.txt
> +++ b/Documentation/ioctl/ioctl-number.txt
> @@ -303,6 +303,7 @@ Code  Seq#(hex)	Include File		Comments
>  					<mailto:buk@xxxxxxxxxxx>
>  0xA0	all	linux/sdp/sdp.h		Industrial Device Project
>  					<mailto:kenji@xxxxxxxxxxx>
> +0xA1	0	linux/vtpm_proxy.h	TPM Emulator Proxy Driver
>  0xA2	00-0F	arch/tile/include/asm/hardwall.h
>  0xA3	80-8F	Port ACL		in development:
>  					<mailto:tlewis@xxxxxxxxxxxxxx>
> diff --git a/Documentation/tpm/tpm_vtpm_proxy.txt b/Documentation/tpm/tpm_vtpm_proxy.txt
> new file mode 100644
> index 0000000..30d1902
> --- /dev/null
> +++ b/Documentation/tpm/tpm_vtpm_proxy.txt
> @@ -0,0 +1,71 @@
> +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.
> -- 
> 2.4.3
>