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Message-ID: <56BCF84E.50808@infradead.org>
Date: Thu, 11 Feb 2016 13:08:30 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Jens Wiklander <jens.wiklander@...aro.org>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
devicetree@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: valentin.manea@...wei.com, jean-michel.delorme@...com,
emmanuel.michel@...com, javier@...igon.com,
Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
Mark Rutland <mark.rutland@....com>,
Michal Simek <michal.simek@...inx.com>,
Rob Herring <robh+dt@...nel.org>,
Will Deacon <will.deacon@....com>,
Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v8 4/4] Documentation: tee subsystem and op-tee driver
On 02/11/16 09:14, Jens Wiklander wrote:
> Signed-off-by: Jens Wiklander <jens.wiklander@...aro.org>
> ---
> Documentation/00-INDEX | 2 +
> Documentation/tee.txt | 117 +++++++++++++++++++++++++++++++++++++++++++++++++
> MAINTAINERS | 1 +
> 3 files changed, 120 insertions(+)
> create mode 100644 Documentation/tee.txt
> diff --git a/Documentation/tee.txt b/Documentation/tee.txt
> new file mode 100644
> index 0000000..4ac91d2
> --- /dev/null
> +++ b/Documentation/tee.txt
> @@ -0,0 +1,117 @@
> +TEE subsystem
> +This document describes the TEE subsystem in Linux
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 anymore
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
end with '.'
> +
> +- TEE_IOC_INVOKE invokes a function in a Trusted Application
ditto
> +
> +- TEE_IOC_CANCEL may cancel an ongoing TEE_IOC_OPEN_SESSION or TEE_IOC_INVOKE
ditto
> +
> +- TEE_IOC_CLOSE_SESSION closes a session to a Trusted Application
ditto
> +
> +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.
--
~Randy
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