mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-29 23:53:55 +08:00
4297739f2b
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - adjust identation of titles; - mark ascii artwork as a literal block; - adjust references. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
128 lines
5.2 KiB
Plaintext
128 lines
5.2 KiB
Plaintext
=============
|
|
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.
|