OP-TEE December 2023

op-tee@lists.trustedfirmware.org

12 participants
15 discussions

[PATCH v3] Documentation: Destage TEE subsystem documentation

by Sumit Garg

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. Acked-by: Rijo Thomas <Rijo-john.Thomas(a)amd.com> Acked-by: Jens Wiklander <jens.wiklander(a)linaro.org> Signed-off-by: Sumit Garg <sumit.garg(a)linaro.org> --- Changes in v3: - Rebased to docs-next - Fixed dangling references to Documentation/staging/tee.rst. - Applied tags. 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 ++++ .../security/keys/trusted-encrypted.rst | 2 +- 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 +- drivers/tee/optee/Kconfig | 2 +- 14 files changed, 410 insertions(+), 368 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 48bd9921d937..9511db303446 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -112,6 +112,7 @@ available subsections can be seen below. hte/index wmi dpll + 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/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst index 9bc9db8ec651..e989b9802f92 100644 --- a/Documentation/security/keys/trusted-encrypted.rst +++ b/Documentation/security/keys/trusted-encrypted.rst @@ -88,7 +88,7 @@ safe. (2) TEE TEEs have well-documented, standardized client interface and APIs. For - more details refer to ``Documentation/staging/tee.rst``. + more details refer to ``Documentation/driver-api/tee.rst``. (3) CAAM 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_mode… diff --git a/Documentation/subsystem-apis.rst b/Documentation/subsystem-apis.rst index 930dc23998a0..2d353fb8ea26 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_mode… 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 bf8d2ee01580..93174ffc7350 100644 --- a/Documentation/userspace-api/index.rst +++ b/Documentation/userspace-api/index.rst @@ -30,6 +30,7 @@ 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 48fc02d3a1d1..6024d1d5ebf8 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -21351,7 +21351,9 @@ M: Jens Wiklander <jens.wiklander(a)linaro.org> R: Sumit Garg <sumit.garg(a)linaro.org> L: op-tee(a)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 diff --git a/drivers/tee/optee/Kconfig b/drivers/tee/optee/Kconfig index 70898bbd5809..976928641aa6 100644 --- a/drivers/tee/optee/Kconfig +++ b/drivers/tee/optee/Kconfig @@ -23,4 +23,4 @@ config OPTEE_INSECURE_LOAD_IMAGE https://trustedfirmware-a.readthedocs.io/en/latest/threat_model/threat_mode… Additional documentation on kernel security risks are at - Documentation/staging/tee.rst. + Documentation/tee/op-tee.rst. -- 2.34.1

1 year

[PATCH v4] tee: Use iov_iter to better support shared buffer registration

by Arnaud Pouliquen

Currently it's not possible to register kernel buffers with TEE which are allocated via vmalloc. Use iov_iter and associated helper functions to manage the page registration for all type of memories. Suggested-by: Christoph Hellwig <hch(a)infradead.org> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen(a)foss.st.com> --- Update from V3 to V4: - improve commit message, - use import_ubuf() instead of iov_iter_init(), - move shm_get_kernel_pages in register_shm_helper, - put back untagged_addr in register_shm_helper(), - move the comment related to pin pages from shm_get_kernel_pages() to register_shm_helper(). Update from V2 to V3: - break lines longer than 80 columns. Update from V1 to V2: - replace ITER_SOURCE by ITER_DEST flag in tee_shm_register_user_buf(), - replace IS_ERR_OR NULL(shm) by IS_ERR(shm) in tee_shm_register_user_buf(). V1: The support of buffer registration allocated with vmalloc is no more available since c83900393aa1 ("tee: Remove vmalloc page support"). This patch is an alternative to a revert and resulted from a discussion with Christopher Hellwig [1]. This patch has been tested using xtest tool in optee qemu environment [2] and using the series related to the remoteproc tee that should be proposed soon [3]. References: [1] https://lore.kernel.org/linux-arm-kernel/18a8528d-7d9d-6ed0-0045-5ee47dd39f… [2] https://optee.readthedocs.io/en/latest/building/devices/qemu.html#build-ins… [3] https://lore.kernel.org/linux-arm-kernel/18a8528d-7d9d-6ed0-0045-5ee47dd39f… --- drivers/tee/tee_shm.c | 83 ++++++++++++++++++++++++------------------- 1 file changed, 46 insertions(+), 37 deletions(-) diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c index 673cf0359494..ac73e8143233 100644 --- a/drivers/tee/tee_shm.c +++ b/drivers/tee/tee_shm.c @@ -22,23 +22,12 @@ static void shm_put_kernel_pages(struct page **pages, size_t page_count) put_page(pages[n]); } -static int shm_get_kernel_pages(unsigned long start, size_t page_count, - struct page **pages) +static void shm_get_kernel_pages(struct page **pages, size_t page_count) { - struct page *page; size_t n; - if (WARN_ON_ONCE(is_vmalloc_addr((void *)start) || - is_kmap_addr((void *)start))) - return -EINVAL; - - page = virt_to_page((void *)start); - for (n = 0; n < page_count; n++) { - pages[n] = page + n; + for (n = 0; n < page_count; n++) get_page(pages[n]); - } - - return page_count; } static void release_registered_pages(struct tee_shm *shm) @@ -214,13 +203,14 @@ struct tee_shm *tee_shm_alloc_priv_buf(struct tee_context *ctx, size_t size) EXPORT_SYMBOL_GPL(tee_shm_alloc_priv_buf); static struct tee_shm * -register_shm_helper(struct tee_context *ctx, unsigned long addr, - size_t length, u32 flags, int id) +register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags, + int id) { struct tee_device *teedev = ctx->teedev; struct tee_shm *shm; - unsigned long start; - size_t num_pages; + unsigned long start, addr; + size_t num_pages, off; + ssize_t len; void *ret; int rc; @@ -245,31 +235,38 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr, shm->flags = flags; shm->ctx = ctx; shm->id = id; - addr = untagged_addr(addr); + addr = untagged_addr((unsigned long)iter_iov_addr(iter)); start = rounddown(addr, PAGE_SIZE); - shm->offset = addr - start; - shm->size = length; - num_pages = (roundup(addr + length, PAGE_SIZE) - start) / PAGE_SIZE; + num_pages = iov_iter_npages(iter, INT_MAX); + if (!num_pages) { + ret = ERR_PTR(-ENOMEM); + goto err_ctx_put; + } + shm->pages = kcalloc(num_pages, sizeof(*shm->pages), GFP_KERNEL); if (!shm->pages) { ret = ERR_PTR(-ENOMEM); goto err_free_shm; } - if (flags & TEE_SHM_USER_MAPPED) - rc = pin_user_pages_fast(start, num_pages, FOLL_WRITE, - shm->pages); - else - rc = shm_get_kernel_pages(start, num_pages, shm->pages); - if (rc > 0) - shm->num_pages = rc; - if (rc != num_pages) { - if (rc >= 0) - rc = -ENOMEM; - ret = ERR_PTR(rc); - goto err_put_shm_pages; + len = iov_iter_extract_pages(iter, &shm->pages, LONG_MAX, num_pages, 0, + &off); + if (unlikely(len <= 0)) { + ret = len ? ERR_PTR(len) : ERR_PTR(-ENOMEM); + goto err_free_shm_pages; } + /* + * iov_iter_extract_kvec_pages does not get reference on the pages, + * get a pin on them. + */ + if (iov_iter_is_kvec(iter)) + shm_get_kernel_pages(shm->pages, num_pages); + + shm->offset = off; + shm->size = len; + shm->num_pages = num_pages; + rc = teedev->desc->ops->shm_register(ctx, shm, shm->pages, shm->num_pages, start); if (rc) { @@ -279,10 +276,11 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr, return shm; err_put_shm_pages: - if (flags & TEE_SHM_USER_MAPPED) + if (!iov_iter_is_kvec(iter)) unpin_user_pages(shm->pages, shm->num_pages); else shm_put_kernel_pages(shm->pages, shm->num_pages); +err_free_shm_pages: kfree(shm->pages); err_free_shm: kfree(shm); @@ -307,8 +305,9 @@ struct tee_shm *tee_shm_register_user_buf(struct tee_context *ctx, u32 flags = TEE_SHM_USER_MAPPED | TEE_SHM_DYNAMIC; struct tee_device *teedev = ctx->teedev; struct tee_shm *shm; + struct iov_iter iter; void *ret; - int id; + int id, err; if (!access_ok((void __user *)addr, length)) return ERR_PTR(-EFAULT); @@ -319,7 +318,11 @@ struct tee_shm *tee_shm_register_user_buf(struct tee_context *ctx, if (id < 0) return ERR_PTR(id); - shm = register_shm_helper(ctx, addr, length, flags, id); + err = import_ubuf(ITER_DEST, (void __user *)addr, length, &iter); + if (err) + return ERR_PTR(err); + + shm = register_shm_helper(ctx, &iter, flags, id); if (IS_ERR(shm)) { mutex_lock(&teedev->mutex); idr_remove(&teedev->idr, id); @@ -352,8 +355,14 @@ struct tee_shm *tee_shm_register_kernel_buf(struct tee_context *ctx, void *addr, size_t length) { u32 flags = TEE_SHM_DYNAMIC; + struct kvec kvec; + struct iov_iter iter; + + kvec.iov_base = addr; + kvec.iov_len = length; + iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, length); - return register_shm_helper(ctx, (unsigned long)addr, length, flags, -1); + return register_shm_helper(ctx, &iter, flags, -1); } EXPORT_SYMBOL_GPL(tee_shm_register_kernel_buf); -- 2.25.1

1 year

optee: os: toolchains would include linux target macros likes __linux__

by Randy Li

Hello I wonder why Optee OS would use a linux target toolchains but not a bare metal target(none os)? gcc-arm-10.3-2021.07-x86_64-aarch64-none-linux-gnu/bin/aarch64-none-linux-gnu-gcc -dM -E - < /dev/null|grep linux #define __linux 1 #define __gnu_linux__ 1 #define linux 1 #define __linux__ 1 That makes hard to share a header files between Linux kernel and Optee. We like to pass some structure in SHM, but optee don't have all those Linux types likes <linux/types.h>. If optee didn't choose the toolchains for the Linux, we could easily decide which part would use for Client Agent(Linux kernel) side or TEE OS side. Why we don't use bare metal toolchains ? Thank you Randy Li

1 year

Could secure monitor let op-tee handle secure interrupter?

by Randy Li

Hello I was wondering whether the current op-tee os support this that secure monitor would trigger the op-tee to handle the native interrupter without forwarding it to the REE? If the answer is yes, could it lead to a dead lock when the linux kernel is holding a spinlock(usually irq is disabled in that CPU core) ? I didn't find much about how should we handle the secure interrupter from document, the general way seems to either forward it to REE or just don't use the secure interrupter at all. Let the REE handle the interrupter may not be a good idea, since the device could we should ack the interrupter in it, is protected by the trustzone, we need to switch CPU to secure mode to handle this tiny task. I wish I could know more solution about the interrupter here. Sincerely Randy

1 year

[PATCH v3 0/2] OP-TEE kernel private shared memory optimizations

by Jens Wiklander

Hi, This patch set optimizes OP-TEE driver private shared memory allocated as dynamic shared memory (not from the static shared memory pool). The first patch handles kernel private RPC allocatations larger than one page and the second changes from alloc_pages_exact() instead of alloc_pages() for more efficient memory usage. v1->v2: * Split into two patches as requested v2->v3: * Simplified optee_pool_op_alloc_helper() by always doing the same thing Thanks, Jens Jens Wiklander (2): optee: add page list to kernel private shared memory optee: allocate shared memory with alloc_pages_exact() drivers/tee/optee/core.c | 44 +++++++++++++++++++----------------- drivers/tee/optee/smc_abi.c | 45 +++++++++++++++++-------------------- 2 files changed, 44 insertions(+), 45 deletions(-) base-commit: 05d3ef8bba77c1b5f98d941d8b2d4aeab8118ef1 -- 2.34.1

1 year

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OP-TEE December 2023