[PATCH v14 4/5] Documentation: tee subsystem and op-tee driver

[Scott Branden]

Hi Jens,

Documentation looks good.

On 17-01-18 04:58 AM, Jens Wiklander wrote:
> Acked-by: Andreas Dannenberg <dannenberg at ti.com>
> Signed-off-by: Jens Wiklander <jens.wiklander at linaro.org>
Acked-by: Scott Branden <scott.branden at broadcom.com>
> ---
>  Documentation/00-INDEX |   2 +
>  Documentation/tee.txt  | 118 +++++++++++++++++++++++++++++++++++++++++++++++++
>  MAINTAINERS            |   1 +
>  3 files changed, 121 insertions(+)
>  create mode 100644 Documentation/tee.txt
>
> diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
> index c8a8eb1a2b11..fc6a3cb83d97 100644
> --- a/Documentation/00-INDEX
> +++ b/Documentation/00-INDEX
> @@ -412,6 +412,8 @@ sysctl/
>  	- directory with info on the /proc/sys/* files.
>  target/
>  	- directory with info on generating TCM v4 fabric .ko modules
> +tee.txt
> +	- info on the TEE subsystem and drivers
>  this_cpu_ops.txt
>  	- List rationale behind and the way to use this_cpu operations.
>  thermal/
> diff --git a/Documentation/tee.txt b/Documentation/tee.txt
> new file mode 100644
> index 000000000000..718599357596
> --- /dev/null
> +++ b/Documentation/tee.txt
> @@ -0,0 +1,118 @@
> +TEE subsystem
> +This document describes the TEE subsystem in Linux.
> +
> +A TEE (Trusted Execution Environment) is a trusted OS running in some
> +secure environment, for example, TrustZone on ARM CPUs, or a separate
> +secure co-processor etc. A TEE driver handles the details needed to
> +communicate with the TEE.
> +
> +This subsystem deals with:
> +
> +- Registration of TEE drivers
> +
> +- Managing shared memory between Linux and the TEE
> +
> +- Providing a generic API to the TEE
> +
> +The TEE interface
> +=================
> +
> +include/uapi/linux/tee.h defines the generic interface to a TEE.
> +
> +User space (the client) connects to the driver by opening /dev/tee[0-9]* or
> +/dev/teepriv[0-9]*.
> +
> +- TEE_IOC_SHM_ALLOC allocates shared memory and returns a file descriptor
> +  which user space can mmap. When user space doesn't need the file
> +  descriptor any more, it should be closed. When shared memory isn't needed
> +  any longer it should be unmapped with munmap() to allow the reuse of
> +  memory.
> +
> +- TEE_IOC_VERSION lets user space know which TEE this driver handles and
> +  the its capabilities.
> +
> +- TEE_IOC_OPEN_SESSION opens a new session to a Trusted Application.
> +
> +- TEE_IOC_INVOKE invokes a function in a Trusted Application.
> +
> +- TEE_IOC_CANCEL may cancel an ongoing TEE_IOC_OPEN_SESSION or TEE_IOC_INVOKE.
> +
> +- TEE_IOC_CLOSE_SESSION closes a session to a Trusted Application.
> +
> +There are two classes of clients, normal clients and supplicants. The latter is
> +a helper process for the TEE to access resources in Linux, for example file
> +system access. A normal client opens /dev/tee[0-9]* and a supplicant opens
> +/dev/teepriv[0-9].
> +
> +Much of the communication between clients and the TEE is opaque to the
> +driver. The main job for the driver is to receive requests from the
> +clients, forward them to the TEE and send back the results. In the case of
> +supplicants the communication goes in the other direction, the TEE sends
> +requests to the supplicant which then sends back the result.
> +
> +OP-TEE driver
> +=============
> +
> +The OP-TEE driver handles OP-TEE [1] based TEEs. Currently it is only the ARM
> +TrustZone based OP-TEE solution that is supported.
> +
> +Lowest level of communication with OP-TEE builds on ARM SMC Calling
> +Convention (SMCCC) [2], which is the foundation for OP-TEE's SMC interface
> +[3] used internally by the driver. Stacked on top of that is OP-TEE Message
> +Protocol [4].
> +
> +OP-TEE SMC interface provides the basic functions required by SMCCC and some
> +additional functions specific for OP-TEE. The most interesting functions are:
> +
> +- OPTEE_SMC_FUNCID_CALLS_UID (part of SMCCC) returns the version information
> +  which is then returned by TEE_IOC_VERSION
> +
> +- OPTEE_SMC_CALL_GET_OS_UUID returns the particular OP-TEE implementation, used
> +  to tell, for instance, a TrustZone OP-TEE apart from an OP-TEE running on a
> +  separate secure co-processor.
> +
> +- OPTEE_SMC_CALL_WITH_ARG drives the OP-TEE message protocol
> +
> +- OPTEE_SMC_GET_SHM_CONFIG lets the driver and OP-TEE agree on which memory
> +  range to used for shared memory between Linux and OP-TEE.
> +
> +The GlobalPlatform TEE Client API [5] is implemented on top of the generic
> +TEE API.
> +
> +Picture of the relationship between the different components in the
> +OP-TEE architecture.
> +
> +    User space                  Kernel                   Secure world
> +    ~~~~~~~~~~                  ~~~~~~                   ~~~~~~~~~~~~
> + +--------+                                             +-------------+
> + | Client |                                             | Trusted     |
> + +--------+                                             | Application |
> +    /\                                                  +-------------+
> +    || +----------+                                           /\
> +    || |tee-      |                                           ||
> +    || |supplicant|                                           \/
> +    || +----------+                                     +-------------+
> +    \/      /\                                          | TEE Internal|
> + +-------+  ||                                          | API         |
> + + TEE   |  ||            +--------+--------+           +-------------+
> + | Client|  ||            | TEE    | OP-TEE |           | OP-TEE      |
> + | API   |  \/            | subsys | driver |           | Trusted OS  |
> + +-------+----------------+----+-------+----+-----------+-------------+
> + |      Generic TEE API        |       |     OP-TEE MSG               |
> + |      IOCTL (TEE_IOC_*)      |       |     SMCCC (OPTEE_SMC_CALL_*) |
> + +-----------------------------+       +------------------------------+
> +
> +RPC (Remote Procedure Call) are requests from secure world to kernel driver
> +or tee-supplicant. An RPC is identified by a special range of SMCCC return
> +values from OPTEE_SMC_CALL_WITH_ARG. RPC messages which are intended for the
> +kernel are handled by the kernel driver. Other RPC messages will be forwarded to
> +tee-supplicant without further involvement of the driver, except switching
> +shared memory buffer representation.
> +
> +References:
> +[1] https://github.com/OP-TEE/optee_os
> +[2] http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
> +[3] drivers/tee/optee/optee_smc.h
> +[4] drivers/tee/optee/optee_msg.h
> +[5] http://www.globalplatform.org/specificationsdevice.asp look for
> +    "TEE Client API Specification v1.0" and click download.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 975fd339c026..eec9bee0d752 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10895,6 +10895,7 @@ S:	Maintained
>  F:	include/linux/tee_drv.h
>  F:	include/uapi/linux/tee.h
>  F:	drivers/tee/
> +F:	Documentation/tee.txt
>
>  THUNDERBOLT DRIVER
>  M:	Andreas Noever <andreas.noever at gmail.com>
>