Add a separate documentation directory for TEE subsystem since it is a standalone subsystem which already offers devices consumed by multiple different subsystem drivers.
Split overall TEE subsystem documentation modularly where: - The userspace API has been moved to Documentation/userspace-api/tee.rst. - The driver API has been moved to Documentation/driver-api/tee.rst. - The first module covers the overview of TEE subsystem. - The further modules are dedicated to different TEE implementations like: - OP-TEE - AMD-TEE - and so on for future TEE implementation support.
Signed-off-by: Sumit Garg sumit.garg@linaro.org ---
Changes in v2: - Move userspace API to Documentation/userspace-api/tee.rst. - Move driver API to Documentation/driver-api/tee.rst.
Documentation/driver-api/index.rst | 1 + Documentation/driver-api/tee.rst | 66 +++++ Documentation/staging/index.rst | 1 - Documentation/staging/tee.rst | 364 -------------------------- Documentation/subsystem-apis.rst | 1 + Documentation/tee/amd-tee.rst | 90 +++++++ Documentation/tee/index.rst | 19 ++ Documentation/tee/op-tee.rst | 166 ++++++++++++ Documentation/tee/tee.rst | 22 ++ Documentation/userspace-api/index.rst | 1 + Documentation/userspace-api/tee.rst | 39 +++ MAINTAINERS | 4 +- 12 files changed, 408 insertions(+), 366 deletions(-) create mode 100644 Documentation/driver-api/tee.rst delete mode 100644 Documentation/staging/tee.rst create mode 100644 Documentation/tee/amd-tee.rst create mode 100644 Documentation/tee/index.rst create mode 100644 Documentation/tee/op-tee.rst create mode 100644 Documentation/tee/tee.rst create mode 100644 Documentation/userspace-api/tee.rst
diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index 1e16a40da3ba..b4214d98d7b5 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -114,6 +114,7 @@ available subsections can be seen below. zorro hte/index wmi + tee
.. only:: subproject and html
diff --git a/Documentation/driver-api/tee.rst b/Documentation/driver-api/tee.rst new file mode 100644 index 000000000000..5eaeb8103988 --- /dev/null +++ b/Documentation/driver-api/tee.rst @@ -0,0 +1,66 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============================================== +TEE (Trusted Execution Environment) driver API +=============================================== + +Kernel provides a TEE bus infrastructure where a Trusted Application is +represented as a device identified via Universally Unique Identifier (UUID) and +client drivers register a table of supported device UUIDs. + +TEE bus infrastructure registers following APIs: + +match(): + iterates over the client driver UUID table to find a corresponding + match for device UUID. If a match is found, then this particular device is + probed via corresponding probe API registered by the client driver. This + process happens whenever a device or a client driver is registered with TEE + bus. + +uevent(): + notifies user-space (udev) whenever a new device is registered on + TEE bus for auto-loading of modularized client drivers. + +TEE bus device enumeration is specific to underlying TEE implementation, so it +is left open for TEE drivers to provide corresponding implementation. + +Then TEE client driver can talk to a matched Trusted Application using APIs +listed in include/linux/tee_drv.h. + +TEE client driver example +------------------------- + +Suppose a TEE client driver needs to communicate with a Trusted Application +having UUID: ``ac6a4085-0e82-4c33-bf98-8eb8e118b6c2``, so driver registration +snippet would look like:: + + static const struct tee_client_device_id client_id_table[] = { + {UUID_INIT(0xac6a4085, 0x0e82, 0x4c33, + 0xbf, 0x98, 0x8e, 0xb8, 0xe1, 0x18, 0xb6, 0xc2)}, + {} + }; + + MODULE_DEVICE_TABLE(tee, client_id_table); + + static struct tee_client_driver client_driver = { + .id_table = client_id_table, + .driver = { + .name = DRIVER_NAME, + .bus = &tee_bus_type, + .probe = client_probe, + .remove = client_remove, + }, + }; + + static int __init client_init(void) + { + return driver_register(&client_driver.driver); + } + + static void __exit client_exit(void) + { + driver_unregister(&client_driver.driver); + } + + module_init(client_init); + module_exit(client_exit); diff --git a/Documentation/staging/index.rst b/Documentation/staging/index.rst index ded8254bc0d7..71592f3ce89b 100644 --- a/Documentation/staging/index.rst +++ b/Documentation/staging/index.rst @@ -12,5 +12,4 @@ Unsorted Documentation rpmsg speculation static-keys - tee xz diff --git a/Documentation/staging/tee.rst b/Documentation/staging/tee.rst deleted file mode 100644 index 22baa077a3b9..000000000000 --- a/Documentation/staging/tee.rst +++ /dev/null @@ -1,364 +0,0 @@ -============= -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 - 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. - -The TEE kernel interface -======================== - -Kernel provides a TEE bus infrastructure where a Trusted Application is -represented as a device identified via Universally Unique Identifier (UUID) and -client drivers register a table of supported device UUIDs. - -TEE bus infrastructure registers following APIs: - -match(): - iterates over the client driver UUID table to find a corresponding - match for device UUID. If a match is found, then this particular device is - probed via corresponding probe API registered by the client driver. This - process happens whenever a device or a client driver is registered with TEE - bus. - -uevent(): - notifies user-space (udev) whenever a new device is registered on - TEE bus for auto-loading of modularized client drivers. - -TEE bus device enumeration is specific to underlying TEE implementation, so it -is left open for TEE drivers to provide corresponding implementation. - -Then TEE client driver can talk to a matched Trusted Application using APIs -listed in include/linux/tee_drv.h. - -TEE client driver example -------------------------- - -Suppose a TEE client driver needs to communicate with a Trusted Application -having UUID: ``ac6a4085-0e82-4c33-bf98-8eb8e118b6c2``, so driver registration -snippet would look like:: - - static const struct tee_client_device_id client_id_table[] = { - {UUID_INIT(0xac6a4085, 0x0e82, 0x4c33, - 0xbf, 0x98, 0x8e, 0xb8, 0xe1, 0x18, 0xb6, 0xc2)}, - {} - }; - - MODULE_DEVICE_TABLE(tee, client_id_table); - - static struct tee_client_driver client_driver = { - .id_table = client_id_table, - .driver = { - .name = DRIVER_NAME, - .bus = &tee_bus_type, - .probe = client_probe, - .remove = client_remove, - }, - }; - - static int __init client_init(void) - { - return driver_register(&client_driver.driver); - } - - static void __exit client_exit(void) - { - driver_unregister(&client_driver.driver); - } - - module_init(client_init); - module_exit(client_exit); - -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. - -OP-TEE device enumeration -------------------------- - -OP-TEE provides a pseudo Trusted Application: drivers/tee/optee/device.c in -order to support device enumeration. In other words, OP-TEE driver invokes this -application to retrieve a list of Trusted Applications which can be registered -as devices on the TEE bus. - -OP-TEE notifications --------------------- - -There are two kinds of notifications that secure world can use to make -normal world aware of some event. - -1. Synchronous notifications delivered with ``OPTEE_RPC_CMD_NOTIFICATION`` - using the ``OPTEE_RPC_NOTIFICATION_SEND`` parameter. -2. Asynchronous notifications delivered with a combination of a non-secure - edge-triggered interrupt and a fast call from the non-secure interrupt - handler. - -Synchronous notifications are limited by depending on RPC for delivery, -this is only usable when secure world is entered with a yielding call via -``OPTEE_SMC_CALL_WITH_ARG``. This excludes such notifications from secure -world interrupt handlers. - -An asynchronous notification is delivered via a non-secure edge-triggered -interrupt to an interrupt handler registered in the OP-TEE driver. The -actual notification value are retrieved with the fast call -``OPTEE_SMC_GET_ASYNC_NOTIF_VALUE``. Note that one interrupt can represent -multiple notifications. - -One notification value ``OPTEE_SMC_ASYNC_NOTIF_VALUE_DO_BOTTOM_HALF`` has a -special meaning. When this value is received it means that normal world is -supposed to make a yielding call ``OPTEE_MSG_CMD_DO_BOTTOM_HALF``. This -call is done from the thread assisting the interrupt handler. This is a -building block for OP-TEE OS in secure world to implement the top half and -bottom half style of device drivers. - -OPTEE_INSECURE_LOAD_IMAGE Kconfig option ----------------------------------------- - -The OPTEE_INSECURE_LOAD_IMAGE Kconfig option enables the ability to load the -BL32 OP-TEE image from the kernel after the kernel boots, rather than loading -it from the firmware before the kernel boots. This also requires enabling the -corresponding option in Trusted Firmware for Arm. The Trusted Firmware for Arm -documentation [8] explains the security threat associated with enabling this as -well as mitigations at the firmware and platform level. - -There are additional attack vectors/mitigations for the kernel that should be -addressed when using this option. - -1. Boot chain security. - - * Attack vector: Replace the OP-TEE OS image in the rootfs to gain control of - the system. - - * Mitigation: There must be boot chain security that verifies the kernel and - rootfs, otherwise an attacker can modify the loaded OP-TEE binary by - modifying it in the rootfs. - -2. Alternate boot modes. - - * Attack vector: Using an alternate boot mode (i.e. recovery mode), the - OP-TEE driver isn't loaded, leaving the SMC hole open. - - * Mitigation: If there are alternate methods of booting the device, such as a - recovery mode, it should be ensured that the same mitigations are applied - in that mode. - -3. Attacks prior to SMC invocation. - - * Attack vector: Code that is executed prior to issuing the SMC call to load - OP-TEE can be exploited to then load an alternate OS image. - - * Mitigation: The OP-TEE driver must be loaded before any potential attack - vectors are opened up. This should include mounting of any modifiable - filesystems, opening of network ports or communicating with external - devices (e.g. USB). - -4. Blocking SMC call to load OP-TEE. - - * Attack vector: Prevent the driver from being probed, so the SMC call to - load OP-TEE isn't executed when desired, leaving it open to being executed - later and loading a modified OS. - - * Mitigation: It is recommended to build the OP-TEE driver as builtin driver - rather than as a module to prevent exploits that may cause the module to - not be loaded. - -AMD-TEE driver -============== - -The AMD-TEE driver handles the communication with AMD's TEE environment. The -TEE environment is provided by AMD Secure Processor. - -The AMD Secure Processor (formerly called Platform Security Processor or PSP) -is a dedicated processor that features ARM TrustZone technology, along with a -software-based Trusted Execution Environment (TEE) designed to enable -third-party Trusted Applications. This feature is currently enabled only for -APUs. - -The following picture shows a high level overview of AMD-TEE:: - - | - x86 | - | - User space (Kernel space) | AMD Secure Processor (PSP) - ~~~~~~~~~~ ~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~~~~~~ - | - +--------+ | +-------------+ - | Client | | | Trusted | - +--------+ | | Application | - /\ | +-------------+ - || | /\ - || | || - || | / - || | +----------+ - || | | TEE | - || | | Internal | - / | | API | - +---------+ +-----------+---------+ +----------+ - | TEE | | TEE | AMD-TEE | | AMD-TEE | - | Client | | subsystem | driver | | Trusted | - | API | | | | | OS | - +---------+-----------+----+------+---------+---------+----------+ - | Generic TEE API | | ASP | Mailbox | - | IOCTL (TEE_IOC_*) | | driver | Register Protocol | - +--------------------------+ +---------+--------------------+ - -At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the -CPU to PSP mailbox register to submit commands to the PSP. The format of the -command buffer is opaque to the ASP driver. It's role is to submit commands to -the secure processor and return results to AMD-TEE driver. The interface -between AMD-TEE driver and AMD Secure Processor driver can be found in [6]. - -The AMD-TEE driver packages the command buffer payload for processing in TEE. -The command buffer format for the different TEE commands can be found in [7]. - -The TEE commands supported by AMD-TEE Trusted OS are: - -* TEE_CMD_ID_LOAD_TA - loads a Trusted Application (TA) binary into - TEE environment. -* TEE_CMD_ID_UNLOAD_TA - unloads TA binary from TEE environment. -* TEE_CMD_ID_OPEN_SESSION - opens a session with a loaded TA. -* TEE_CMD_ID_CLOSE_SESSION - closes session with loaded TA -* TEE_CMD_ID_INVOKE_CMD - invokes a command with loaded TA -* TEE_CMD_ID_MAP_SHARED_MEM - maps shared memory -* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory - -AMD-TEE Trusted OS is the firmware running on AMD Secure Processor. - -The AMD-TEE driver registers itself with TEE subsystem and implements the -following driver function callbacks: - -* get_version - returns the driver implementation id and capability. -* open - sets up the driver context data structure. -* release - frees up driver resources. -* open_session - loads the TA binary and opens session with loaded TA. -* close_session - closes session with loaded TA and unloads it. -* invoke_func - invokes a command with loaded TA. - -cancel_req driver callback is not supported by AMD-TEE. - -The GlobalPlatform TEE Client API [5] can be used by the user space (client) to -talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening -a session, invoking commands and closing session with TA. - -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. - -[6] include/linux/psp-tee.h - -[7] drivers/tee/amdtee/amdtee_if.h - -[8] https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model... diff --git a/Documentation/subsystem-apis.rst b/Documentation/subsystem-apis.rst index 90a0535a932a..1666f11de8df 100644 --- a/Documentation/subsystem-apis.rst +++ b/Documentation/subsystem-apis.rst @@ -86,3 +86,4 @@ Storage interfaces misc-devices/index peci/index wmi/index + tee/index diff --git a/Documentation/tee/amd-tee.rst b/Documentation/tee/amd-tee.rst new file mode 100644 index 000000000000..51500fde7038 --- /dev/null +++ b/Documentation/tee/amd-tee.rst @@ -0,0 +1,90 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================= +AMD-TEE (AMD's Trusted Execution Environment) +============================================= + +The AMD-TEE driver handles the communication with AMD's TEE environment. The +TEE environment is provided by AMD Secure Processor. + +The AMD Secure Processor (formerly called Platform Security Processor or PSP) +is a dedicated processor that features ARM TrustZone technology, along with a +software-based Trusted Execution Environment (TEE) designed to enable +third-party Trusted Applications. This feature is currently enabled only for +APUs. + +The following picture shows a high level overview of AMD-TEE:: + + | + x86 | + | + User space (Kernel space) | AMD Secure Processor (PSP) + ~~~~~~~~~~ ~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~~~~~~ + | + +--------+ | +-------------+ + | Client | | | Trusted | + +--------+ | | Application | + /\ | +-------------+ + || | /\ + || | || + || | / + || | +----------+ + || | | TEE | + || | | Internal | + / | | API | + +---------+ +-----------+---------+ +----------+ + | TEE | | TEE | AMD-TEE | | AMD-TEE | + | Client | | subsystem | driver | | Trusted | + | API | | | | | OS | + +---------+-----------+----+------+---------+---------+----------+ + | Generic TEE API | | ASP | Mailbox | + | IOCTL (TEE_IOC_*) | | driver | Register Protocol | + +--------------------------+ +---------+--------------------+ + +At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the +CPU to PSP mailbox register to submit commands to the PSP. The format of the +command buffer is opaque to the ASP driver. It's role is to submit commands to +the secure processor and return results to AMD-TEE driver. The interface +between AMD-TEE driver and AMD Secure Processor driver can be found in [1]. + +The AMD-TEE driver packages the command buffer payload for processing in TEE. +The command buffer format for the different TEE commands can be found in [2]. + +The TEE commands supported by AMD-TEE Trusted OS are: + +* TEE_CMD_ID_LOAD_TA - loads a Trusted Application (TA) binary into + TEE environment. +* TEE_CMD_ID_UNLOAD_TA - unloads TA binary from TEE environment. +* TEE_CMD_ID_OPEN_SESSION - opens a session with a loaded TA. +* TEE_CMD_ID_CLOSE_SESSION - closes session with loaded TA +* TEE_CMD_ID_INVOKE_CMD - invokes a command with loaded TA +* TEE_CMD_ID_MAP_SHARED_MEM - maps shared memory +* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory + +AMD-TEE Trusted OS is the firmware running on AMD Secure Processor. + +The AMD-TEE driver registers itself with TEE subsystem and implements the +following driver function callbacks: + +* get_version - returns the driver implementation id and capability. +* open - sets up the driver context data structure. +* release - frees up driver resources. +* open_session - loads the TA binary and opens session with loaded TA. +* close_session - closes session with loaded TA and unloads it. +* invoke_func - invokes a command with loaded TA. + +cancel_req driver callback is not supported by AMD-TEE. + +The GlobalPlatform TEE Client API [3] can be used by the user space (client) to +talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening +a session, invoking commands and closing session with TA. + +References +========== + +[1] include/linux/psp-tee.h + +[2] drivers/tee/amdtee/amdtee_if.h + +[3] http://www.globalplatform.org/specificationsdevice.asp look for + "TEE Client API Specification v1.0" and click download. diff --git a/Documentation/tee/index.rst b/Documentation/tee/index.rst new file mode 100644 index 000000000000..a23bd08847e5 --- /dev/null +++ b/Documentation/tee/index.rst @@ -0,0 +1,19 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +TEE Subsystem +============= + +.. toctree:: + :maxdepth: 1 + + tee + op-tee + amd-tee + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/tee/op-tee.rst b/Documentation/tee/op-tee.rst new file mode 100644 index 000000000000..b0ac097d5547 --- /dev/null +++ b/Documentation/tee/op-tee.rst @@ -0,0 +1,166 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================================================== +OP-TEE (Open Portable Trusted Execution Environment) +==================================================== + +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. + +OP-TEE device enumeration +------------------------- + +OP-TEE provides a pseudo Trusted Application: drivers/tee/optee/device.c in +order to support device enumeration. In other words, OP-TEE driver invokes this +application to retrieve a list of Trusted Applications which can be registered +as devices on the TEE bus. + +OP-TEE notifications +-------------------- + +There are two kinds of notifications that secure world can use to make +normal world aware of some event. + +1. Synchronous notifications delivered with ``OPTEE_RPC_CMD_NOTIFICATION`` + using the ``OPTEE_RPC_NOTIFICATION_SEND`` parameter. +2. Asynchronous notifications delivered with a combination of a non-secure + edge-triggered interrupt and a fast call from the non-secure interrupt + handler. + +Synchronous notifications are limited by depending on RPC for delivery, +this is only usable when secure world is entered with a yielding call via +``OPTEE_SMC_CALL_WITH_ARG``. This excludes such notifications from secure +world interrupt handlers. + +An asynchronous notification is delivered via a non-secure edge-triggered +interrupt to an interrupt handler registered in the OP-TEE driver. The +actual notification value are retrieved with the fast call +``OPTEE_SMC_GET_ASYNC_NOTIF_VALUE``. Note that one interrupt can represent +multiple notifications. + +One notification value ``OPTEE_SMC_ASYNC_NOTIF_VALUE_DO_BOTTOM_HALF`` has a +special meaning. When this value is received it means that normal world is +supposed to make a yielding call ``OPTEE_MSG_CMD_DO_BOTTOM_HALF``. This +call is done from the thread assisting the interrupt handler. This is a +building block for OP-TEE OS in secure world to implement the top half and +bottom half style of device drivers. + +OPTEE_INSECURE_LOAD_IMAGE Kconfig option +---------------------------------------- + +The OPTEE_INSECURE_LOAD_IMAGE Kconfig option enables the ability to load the +BL32 OP-TEE image from the kernel after the kernel boots, rather than loading +it from the firmware before the kernel boots. This also requires enabling the +corresponding option in Trusted Firmware for Arm. The Trusted Firmware for Arm +documentation [6] explains the security threat associated with enabling this as +well as mitigations at the firmware and platform level. + +There are additional attack vectors/mitigations for the kernel that should be +addressed when using this option. + +1. Boot chain security. + + * Attack vector: Replace the OP-TEE OS image in the rootfs to gain control of + the system. + + * Mitigation: There must be boot chain security that verifies the kernel and + rootfs, otherwise an attacker can modify the loaded OP-TEE binary by + modifying it in the rootfs. + +2. Alternate boot modes. + + * Attack vector: Using an alternate boot mode (i.e. recovery mode), the + OP-TEE driver isn't loaded, leaving the SMC hole open. + + * Mitigation: If there are alternate methods of booting the device, such as a + recovery mode, it should be ensured that the same mitigations are applied + in that mode. + +3. Attacks prior to SMC invocation. + + * Attack vector: Code that is executed prior to issuing the SMC call to load + OP-TEE can be exploited to then load an alternate OS image. + + * Mitigation: The OP-TEE driver must be loaded before any potential attack + vectors are opened up. This should include mounting of any modifiable + filesystems, opening of network ports or communicating with external + devices (e.g. USB). + +4. Blocking SMC call to load OP-TEE. + + * Attack vector: Prevent the driver from being probed, so the SMC call to + load OP-TEE isn't executed when desired, leaving it open to being executed + later and loading a modified OS. + + * Mitigation: It is recommended to build the OP-TEE driver as builtin driver + rather than as a module to prevent exploits that may cause the module to + not be loaded. + +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. + +[6] https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_model... diff --git a/Documentation/tee/tee.rst b/Documentation/tee/tee.rst new file mode 100644 index 000000000000..fd9f8c4ff63d --- /dev/null +++ b/Documentation/tee/tee.rst @@ -0,0 +1,22 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=================================== +TEE (Trusted Execution Environment) +=================================== + +This document describes the TEE subsystem in Linux. + +Overview +======== + +A TEE 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 diff --git a/Documentation/userspace-api/index.rst b/Documentation/userspace-api/index.rst index 72a65db0c498..24ed39735dd3 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -32,6 +32,7 @@ place where this information is gathered. sysfs-platform_profile vduse futex2 + tee
.. only:: subproject and html
diff --git a/Documentation/userspace-api/tee.rst b/Documentation/userspace-api/tee.rst new file mode 100644 index 000000000000..e2368dbc3451 --- /dev/null +++ b/Documentation/userspace-api/tee.rst @@ -0,0 +1,39 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. tee: + +================================================== +TEE (Trusted Execution Environment) Userspace API +================================================== + +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 + 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. diff --git a/MAINTAINERS b/MAINTAINERS index dd5de540ec0b..f20d5fb19ebc 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -21130,7 +21130,9 @@ M: Jens Wiklander jens.wiklander@linaro.org R: Sumit Garg sumit.garg@linaro.org L: op-tee@lists.trustedfirmware.org S: Maintained -F: Documentation/staging/tee.rst +F: Documentation/driver-api/tee.rst +F: Documentation/tee/ +F: Documentation/userspace-api/tee.rst F: drivers/tee/ F: include/linux/tee_drv.h F: include/uapi/linux/tee.h