- OP-TEE - lists.trustedfirmware.org

[PATCH] tee: avoid accessing dma-buf shared memory after put

by Hongyan Xu

param_from_user_memref() obtains a temporary reference to the dma-buf tee_shm wrapper by ID. If closing the shared-memory file descriptor races with the ioctl, this temporary reference can be the wrapper's last one. tee_shm_put() then frees the enclosing tee_shm_dmabuf_ref, but the function still reads ref->parent_shm and ref->offset afterwards. Save the parent pointer and offset before dropping the wrapper reference. The additional parent reference keeps the parent shared memory alive for the parameter list as before. Fixes: 146bf4e75eca ("tee: new ioctl to a register tee_shm from a dmabuf file descriptor") Cc: stable(a)vger.kernel.org Signed-off-by: Hongyan Xu <getshell(a)seu.edu.cn> --- drivers/tee/tee_core.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c index 1aac50c7c1de..489c39d5b35f 100644 --- a/drivers/tee/tee_core.c +++ b/drivers/tee/tee_core.c @@ -397,6 +397,7 @@ static int param_from_user_memref(struct tee_context *ctx, } if (shm->flags & TEE_SHM_DMA_BUF) { + struct tee_shm *parent_shm; struct tee_shm_dmabuf_ref *ref; ref = container_of(shm, struct tee_shm_dmabuf_ref, shm); @@ -409,10 +410,11 @@ static int param_from_user_memref(struct tee_context *ctx, * list instead of the shm we got with * tee_shm_get_from_id() above. */ - refcount_inc(&ref->parent_shm->refcount); - tee_shm_put(shm); - shm = ref->parent_shm; + parent_shm = ref->parent_shm; offs = ref->offset; + refcount_inc(&parent_shm->refcount); + tee_shm_put(shm); + shm = parent_shm; } } } else if (ctx->cap_memref_null) { -- 2.50.1.windows.1

2 weeks, 5 days

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ufs: rpmb: make RPMB usable with OP-TEE key derivation

by Jorge Ramirez-Ortiz

This series makes UFS RPMB work out of the box with an OP-TEE that implements the standard eMMC RPMB key-derivation flow, without requiring any fundamental changes on the OP-TEE side. RPMB provides an authenticated, replay-protected storage area whose security relies on a secret authentication key. In our setup that key is never exposed to the kernel: OP-TEE derives it in the secure world from its hardware-unique key and a device identifier (dev_id) that the RPMB core hands down. OP-TEE's implementation targets eMMC, where dev_id is the 16-byte eMMC CID, and both the fixed length and the raw-CID layout are baked into its key derivation. Two things stand in the way of reusing that same, unmodified OP-TEE flow for UFS RPMB: 1. On a cold boot the very first frame sent to the RPMB well-known LU comes back with a power-on UNIT ATTENTION (ASC 0x29), which the SCSI core reports rather than retries. RPMB has no earlier guaranteed access that could clear the condition first, so RPMB fails on every power cycle. Patch 1 asks the SCSI core to retry the power-on UNIT ATTENTION on the RPMB WLUN. 2. The UFS RPMB id is "<device_id>-R<region>", which is variable length and longer than 16 bytes. Passing it verbatim would tie the derived key to a length OP-TEE does not expect and diverge from the fixed eMMC CID ABI. Patch 2 hashes it into a fixed 16-byte dev_id with blake2s, keeping the key stable and unique per region while matching the eMMC CID layout OP-TEE relies on. The hash algorithm and input string are thus part of the key-derivation ABI and must stay stable. With both patches, UFS RPMB is functional from the first access after a cold boot and derives keys through the existing eMMC-style OP-TEE flow, (requires minimal OP-TEE changes). Jorge Ramirez-Ortiz (2): ufs: rpmb: retry power-on UNIT ATTENTION on the RPMB WLUN ufs: rpmb: use a fixed-length RPMB dev_id drivers/ufs/Kconfig | 1 + drivers/ufs/core/ufs-rpmb.c | 41 ++++++++++++++++++++++++++++++++++--- 2 files changed, 39 insertions(+), 3 deletions(-)

2 weeks, 6 days

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[PATCH v2] tee: remove TZMEM_MODE_GENERIC

by Julian Braha

'select' does not work on config options in a 'choice', so currently it is possible to enable QCOMTEE without QCOM_TZMEM_MODE_SHMBRIDGE, even though this is needed at runtime. There are no users of the generic allocator option, QCOM_TZMEM_MODE_GENERIC, so let's remove it. Then, we can remove the containing choice..endchoice, which allows the 'select' to work as intended. Suggested-by: Arnd Bergmann <arnd(a)arndb.de> Signed-off-by: Julian Braha <julianbraha(a)gmail.com> --- Changes since v1: - remove TZMEM_MODE_GENERIC instead of removing the dead select Link: https://lore.kernel.org/all/20260715092539.18384-1-julianbraha@gmail.com/ --- drivers/firmware/qcom/Kconfig | 26 +++++--------------------- drivers/firmware/qcom/qcom_tzmem.c | 21 --------------------- 2 files changed, 5 insertions(+), 42 deletions(-) diff --git a/drivers/firmware/qcom/Kconfig b/drivers/firmware/qcom/Kconfig index c7f8413ab996..d99e09c5fa18 100644 --- a/drivers/firmware/qcom/Kconfig +++ b/drivers/firmware/qcom/Kconfig @@ -34,33 +34,17 @@ config QCOM_TZMEM tristate select GENERIC_ALLOCATOR -choice - prompt "TrustZone interface memory allocator mode" - depends on QCOM_TZMEM - default QCOM_TZMEM_MODE_GENERIC - help - Selects the mode of the memory allocator providing memory buffers of - suitable format for sharing with the TrustZone. If in doubt, select - 'Generic'. - -config QCOM_TZMEM_MODE_GENERIC - bool "Generic" - help - Use the generic allocator mode. The memory is page-aligned, non-cachable - and physically contiguous. - config QCOM_TZMEM_MODE_SHMBRIDGE - bool "SHM Bridge" + bool "TrustZone interface memory allocator: SHM Bridge" + depends on QCOM_TZMEM help - Use Qualcomm Shared Memory Bridge. The memory has the same alignment as - in the 'Generic' allocator but is also explicitly marked as an SHM Bridge - buffer. + Use Qualcomm Shared Memory Bridge as memory allocator. The memory has the + same alignment as in the 'Generic' allocator but is also explicitly marked + as an SHM Bridge buffer. With this selected, all buffers passed to the TrustZone must be allocated using the TZMem allocator or else the TrustZone will refuse to use them. -endchoice - config QCOM_QSEECOM bool "Qualcomm QSEECOM interface driver" depends on QCOM_SCM=y diff --git a/drivers/firmware/qcom/qcom_tzmem.c b/drivers/firmware/qcom/qcom_tzmem.c index 0635cbeacfc8..5b3e5a3ad1ae 100644 --- a/drivers/firmware/qcom/qcom_tzmem.c +++ b/drivers/firmware/qcom/qcom_tzmem.c @@ -49,25 +49,6 @@ static struct device *qcom_tzmem_dev; static RADIX_TREE(qcom_tzmem_chunks, GFP_ATOMIC); static DEFINE_SPINLOCK(qcom_tzmem_chunks_lock); -#if IS_ENABLED(CONFIG_QCOM_TZMEM_MODE_GENERIC) - -static int qcom_tzmem_init(void) -{ - return 0; -} - -static int qcom_tzmem_init_area(struct qcom_tzmem_area *area) -{ - return 0; -} - -static void qcom_tzmem_cleanup_area(struct qcom_tzmem_area *area) -{ - -} - -#elif IS_ENABLED(CONFIG_QCOM_TZMEM_MODE_SHMBRIDGE) - #include <linux/firmware/qcom/qcom_scm.h> #include <linux/of.h> @@ -189,8 +170,6 @@ static void qcom_tzmem_cleanup_area(struct qcom_tzmem_area *area) kfree(handle); } -#endif /* CONFIG_QCOM_TZMEM_MODE_SHMBRIDGE */ - static int qcom_tzmem_pool_add_memory(struct qcom_tzmem_pool *pool, size_t size, gfp_t gfp) { -- 2.55.0

3 weeks

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[PATCH] tee: qcomtee: user: check the parameter count from the supplicant

by HyeongJun An

The qcomtee_cb_params_to_args() walks the argument array QTEE asked for and indexes the parameter array the supplicant supplied, but it never looks at num_params. A supplicant that answers TEE_IOC_SUPPL_SEND with fewer parameters than the request needs makes that walk read past the end of the allocation. To fix this, reject a response that is too short, the way ureq_select() already does for the receive direction. Fixes: d6e290837e50 ("tee: add Qualcomm TEE driver") Assisted-by: Claude:claude-opus-5 Signed-off-by: HyeongJun An <sammiee5311(a)gmail.com> --- drivers/tee/qcomtee/user_obj.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/tee/qcomtee/user_obj.c b/drivers/tee/qcomtee/user_obj.c index 10452fcc7ccb..2a594ae299da 100644 --- a/drivers/tee/qcomtee/user_obj.c +++ b/drivers/tee/qcomtee/user_obj.c @@ -507,6 +507,10 @@ static int qcomtee_cb_params_to_args(struct qcomtee_arg *u, { int i; + /* Supplicant can not send fewer parameters than requested. */ + if (num_params < qcomtee_args_len(u)) + return -EINVAL; + qcomtee_arg_for_each(i, u) { switch (u[i].type) { case QCOMTEE_ARG_TYPE_IB: -- 2.43.0

3 weeks, 5 days

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OP-TEE Contributions Forum, monthly meeting July 28

by Etienne CARRIERE - foss

Dear all, Tomorrow, Tuesday July 28th, 8am UTC, is the next OP-TEE Public Meeting. For time and connection details, see the calendar at: https://www.trustedfirmware.org/meetings There are no specific topics to the agenda but feel free to join and raise any question or share any topic you want, or just attend in case some discussed topics may interest you. Sorry for the short notice. Regards, Etienne Carriere

4 weeks, 1 day

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[PATCH] tee: remove dead select from kconfig

by Julian Braha

'select' does not work on config options in a 'choice', so currently it is possible to enable QCOMTEE without QCOM_TZMEM_MODE_SHMBRIDGE. This patch removes the select. I've compile-tested this and found that it builds fine without QCOM_TZMEM_MODE_SHMBRIDGE, but I don't have the hardware to runtime test. Please advise if it would be better to make QCOM_TZMEM_MODE_SHMBRIDGE a dependency. This dead select was found by kconfirm, a static analysis tool for Kconfig. Signed-off-by: Julian Braha <julianbraha(a)gmail.com> --- drivers/tee/qcomtee/Kconfig | 1 - 1 file changed, 1 deletion(-) diff --git a/drivers/tee/qcomtee/Kconfig b/drivers/tee/qcomtee/Kconfig index 9f19dee08db4..00e07ed80138 100644 --- a/drivers/tee/qcomtee/Kconfig +++ b/drivers/tee/qcomtee/Kconfig @@ -5,7 +5,6 @@ config QCOMTEE depends on ARCH_QCOM || COMPILE_TEST depends on !CPU_BIG_ENDIAN select QCOM_SCM - select QCOM_TZMEM_MODE_SHMBRIDGE help This option enables the Qualcomm Trusted Execution Environment (QTEE) driver. It provides an API to access services offered by QTEE and -- 2.54.0

1 month

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[PATCH 0/6] Add TEE based client driver for UEFI Secure Application

by Harshal Dev

On Qualcomm SoC based platforms, UEFI stores EFI variables within the Replay Protected Memory Block (RPMB) which is only accessible by the Qualcomm Trusted Execution Environment (QTEE). For Qualcomm platforms without emulated RPMB support, specifically platforms where RPMB is not located within SPI-NOR storage and instead located on UFS/EMMC storage, non-volatile EFI variables can only be set via a callback request from the UEFI Secure Application to the RPMB service running in user-space (within the QTEE supplicant [1]). Unlike the QCOM-TEE driver, the QSEECOM driver (used by the current QSEECOM based uefisecapp) does not support callback requests. And on certain Qualcomm platforms such as the RB3Gen2, attempts to access the QSEECOM interface fail due to lack of support within Qualcomm TEE. On these platforms, a TEE based uefisecapp client driver is required to: 1. Access cached & volatile EFI variables stored in uefisecapp's memory. 2. Ensure persistence of non-volatile EFI variables via writes through the RPMB service hosted in the QTEE supplicant. This series introduces such a uefisecapp TEE client driver for the aforementioned Qualcomm platforms which installs efi-var operations _if_ the QCOMTEE driver registers support for an object-IPC based uefisecapp service on the TEE bus during its probe. Only new QTEE firmware versions available at [2] provide this support. Thus, QCOMTEE now maintains a static list of always-available object-IPC based secure services exposed by QTEE. These services are implemented either within the QTEE kernel or within a pre-loaded Trusted Application (TA) usually loaded by the bootloader. The uefisecapp TA is an example of a preloaded TA loaded by UEFI. A static list is required since QTEE does not yet expose any way to dynamically query and enumerate the services exposed by it. To facilitate object-IPC interactions from the kernel-space, this series also introduces a tee_client_object_invoke_func() to allow invocation of TEE objects similar to the existing tee_client_invoke_func() API exported by the TEE subsystem which allows invocation of TEE functions. Some suporting changes are also introduced to track and handle operations for TEE contexts opened from the kernel-space in the back-end QCOM-TEE driver along with associated changes in user-space libqcomtee via Pull Request [3]. Finally and as previously mentioned, access to the object-IPC based uefisecapp service is restricted on older QTEE firmware versions. A new QTEE firmware release must be picked up from QArtifactory [2] for all upstream supported Qualcomm SoCs to enable access to uefisecapp service via the TEE client driver. This patch series has been validated on Kodiak RB3Gen2 platform with UFS storage by attempting to read/write EFI variables via the efivar tool [4] after mounting the efivarfs filesystem. See [5] for an example. Merge Strategy: This patch series could either be taken from the OP-TEE tree or the QCOM soc tree. I would prefer it to be picked by the OP-TEE tree since all except the uefisecapp TEE client driver patch in this series make changes relevant to the TEE subsystem. It would be great if the QCOM soc tree maintainers can Ack the uefisecapp driver patch. [1] https://github.com/qualcomm/minkipc [2] https://shorturl.at/zQU07 [3] https://github.com/quic/quic-teec/pull/27 [4] https://github.com/rhboot/efivar [5] https://docs.qualcomm.com/doc/80-70020-27/topic/manage_uefi_environment_var… Signed-off-by: Harshal Dev <harshal.dev(a)oss.qualcomm.com> --- Amirreza Zarrabi (2): tee: Add kernel client object invoke helper tee: qcomtee: Allow object invokes from kernel clients Harshal Dev (4): tee: qcomtee: Track the object invocation context tee: Export uuidv5 generation for TEE clients tee: qcomtee: Add support for registering QTEE services on TEE bus firmware: qcom: Add support for TEE based EFI-var client driver MAINTAINERS | 7 + drivers/firmware/qcom/Kconfig | 24 ++ drivers/firmware/qcom/Makefile | 1 + drivers/firmware/qcom/qcom_tee_uefisecapp.c | 525 ++++++++++++++++++++++++++++ drivers/firmware/qcom/qcom_tee_uefisecapp.h | 120 +++++++ drivers/tee/qcomtee/call.c | 218 +++++++++++- drivers/tee/qcomtee/core.c | 9 +- drivers/tee/qcomtee/qcomtee.h | 18 + drivers/tee/qcomtee/qcomtee_msg.h | 1 + drivers/tee/qcomtee/qcomtee_object.h | 16 +- drivers/tee/tee_core.c | 26 +- include/linux/tee_core.h | 15 + include/linux/tee_drv.h | 18 +- 13 files changed, 968 insertions(+), 30 deletions(-) --- base-commit: f3e6330d7fe42b204af05a2dbc68b379e0ad179e change-id: 20260408-qcom_uefisecapp_migrate_qcomtee-13869d45e014 Best regards, -- Harshal Dev <harshal.dev(a)oss.qualcomm.com>

1 month

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[PATCH v3 0/3] tee: add MbedTEE driver

by Xing Loong

This series adds a Linux TEE driver for MbedTEE, a Trusted Execution Environment for embedded systems (https://github.com/mbedtee). Two RPC transports are provided for systems where platform firmware or board configuration has already established the REE/TEE separation before Linux boots: - ARM/ARM64: SMC calls and GIC SPI notifications (TrustZone) - RISC-V: shared-memory ring buffers and IMSIC MSI notifications The driver implements the TEE subsystem interface (tee_driver_ops) and provides GlobalPlatform TEE Client API support, dynamic shared memory registration, and tee-supplicant support for REE filesystem and RPMB operations. The series is structured as follows: [1/3] dt-bindings: vendor-prefixes: add mbedtee [2/3] dt-bindings: firmware: add mbedtee,tee binding [3/3] tee: add MbedTEE driver --- Changes in v3: - 0002: Drop all phandle stub nodes from examples. - 0002: Remove redundant required: - interrupts from then branch. - 0002: Simplify title and description. - Link to v2: https://lore.kernel.org/r/20260702151115.544016-1-xing.xl.loong@gmail.com/ - Link to v1: https://lore.kernel.org/r/20260701132514.186953-1-xing.xl.loong@gmail.com/ Changes in v2: - 0002: Fix DT binding review comments from Krzysztof Kozlowski: - Drop $nodename, "YAML devicetree binding" wording, property descriptions - Rename compatible string to mbedtee,tee - Rename memory regions: rpc-t2r-ring -> t2r-ring, rpc-t2r-shm -> t2r-shm, rpc-r2t-ring -> r2t-ring - Add memory-region / memory-region-names to required - Simplify allOf constraints (drop redundant else-branch items) - Rewrite description to describe hardware/firmware, not the binding or driver - Drop all irrelevant platform nodes (gic, cpus, reserved-memory) - Add maxItems: 1 constraint to interrupts property (Sashiko AI review) - 0003: - Fix supp_release incorrectly aborting unclaimed requests on close - Fix potential tee_shm double-free on supp_recv error path - Fix async RPC ring skip leaving orphaned payload bytes - Fix COMPLETE_TEE retry to also handle transient -ENOMEM on RISC-V - Fix session leak on close_session allocation failure: release kernel resources before sending RPC --- Xing Loong (3): dt-bindings: vendor-prefixes: add mbedtee dt-bindings: firmware: add mbedtee,tee binding tee: add MbedTEE driver .../bindings/firmware/mbedtee,tee.yaml | 109 +++ .../devicetree/bindings/vendor-prefixes.yaml | 2 + Documentation/tee/index.rst | 1 + Documentation/tee/mbedtee.rst | 155 +++++ MAINTAINERS | 9 + drivers/tee/Kconfig | 3 +- drivers/tee/Makefile | 1 + drivers/tee/mbedtee/Kconfig | 20 + drivers/tee/mbedtee/Makefile | 11 + drivers/tee/mbedtee/core.c | 236 +++++++ drivers/tee/mbedtee/mbedtee_drv.h | 269 ++++++++ drivers/tee/mbedtee/mbedtee_msg.h | 219 +++++++ drivers/tee/mbedtee/rpc_callee.c | 618 ++++++++++++++++++ drivers/tee/mbedtee/rpc_callee_arm.c | 91 +++ drivers/tee/mbedtee/rpc_callee_riscv.c | 203 ++++++ drivers/tee/mbedtee/rpc_caller.c | 532 +++++++++++++++ drivers/tee/mbedtee/rpc_caller_arm.c | 66 ++ drivers/tee/mbedtee/rpc_caller_riscv.c | 192 ++++++ drivers/tee/mbedtee/shm_pool.c | 105 +++ drivers/tee/mbedtee/shm_pool.h | 15 + drivers/tee/mbedtee/supp.c | 310 +++++++++ include/uapi/linux/tee.h | 1 + 22 files changed, 3167 insertions(+), 1 deletion(-) create mode 100644 Documentation/devicetree/bindings/firmware/mbedtee,tee.yaml create mode 100644 Documentation/tee/mbedtee.rst create mode 100644 drivers/tee/mbedtee/Kconfig create mode 100644 drivers/tee/mbedtee/Makefile create mode 100644 drivers/tee/mbedtee/core.c create mode 100644 drivers/tee/mbedtee/mbedtee_drv.h create mode 100644 drivers/tee/mbedtee/mbedtee_msg.h create mode 100644 drivers/tee/mbedtee/rpc_callee.c create mode 100644 drivers/tee/mbedtee/rpc_callee_arm.c create mode 100644 drivers/tee/mbedtee/rpc_callee_riscv.c create mode 100644 drivers/tee/mbedtee/rpc_caller.c create mode 100644 drivers/tee/mbedtee/rpc_caller_arm.c create mode 100644 drivers/tee/mbedtee/rpc_caller_riscv.c create mode 100644 drivers/tee/mbedtee/shm_pool.c create mode 100644 drivers/tee/mbedtee/shm_pool.h create mode 100644 drivers/tee/mbedtee/supp.c base-commit: 03e2778d1f11de9260543f969e9e888a1c2bf830 -- 2.43.0

1 month

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[PATCH v1 0/2] ufs: rpmb: make RPMB usable with OP-TEE key derivation

by Jorge Ramirez-Ortiz

This series makes UFS RPMB work out of the box with an OP-TEE that implements the standard eMMC RPMB key-derivation flow, without requiring any fundamental changes on the OP-TEE side. RPMB provides an authenticated, replay-protected storage area whose security relies on a secret authentication key. In our setup that key is never exposed to the kernel: OP-TEE derives it in the secure world from its hardware-unique key and a device identifier (dev_id) that the RPMB core hands down. OP-TEE's implementation targets eMMC, where dev_id is the 16-byte eMMC CID, and both the fixed length and the raw-CID layout are baked into its key derivation. Two things stand in the way of reusing that same, unmodified OP-TEE flow for UFS RPMB: 1. On a cold boot the very first frame sent to the RPMB well-known LU comes back with a power-on UNIT ATTENTION (ASC 0x29), which the SCSI core reports rather than retries. RPMB has no earlier guaranteed access that could clear the condition first, so RPMB fails on every power cycle. Patch 1 asks the SCSI core to retry the power-on UNIT ATTENTION on the RPMB WLUN. 2. The UFS RPMB id is "<device_id>-R<region>", which is variable length and longer than 16 bytes. Passing it verbatim would tie the derived key to a length OP-TEE does not expect and diverge from the fixed eMMC CID ABI. Patch 2 hashes it into a fixed 16-byte dev_id with blake2s, keeping the key stable and unique per region while matching the eMMC CID layout OP-TEE relies on. The hash algorithm and input string are thus part of the key-derivation ABI and must stay stable. With both patches, UFS RPMB is functional from the first access after a cold boot and derives keys through the existing eMMC-style OP-TEE flow, (requires minimal OP-TEE changes pending on the CID proposal done here). Tested on IQ-9075 with Open Firmware [1], pending OP-TEE changes [1]https://ldts.github.io/qcom-buildroot v1: * ufs: rpmb: retry power-on UNIT ATTENTION on the RPMB WLUN: - fix using uses SCMD_FAILURE_ASC_ANY to retry any Unit Attention - fix unused variable * ufs: rpmb: use a fixed-length RPMB dev_id - fix selecting a non-existent Kconfig symbol Jorge Ramirez-Ortiz (2): ufs: rpmb: retry power-on UNIT ATTENTION on the RPMB WLUN ufs: rpmb: use a fixed-length RPMB dev_id drivers/ufs/core/ufs-rpmb.c | 39 ++++++++++++++++++++++++++++++++++--- 1 file changed, 36 insertions(+), 3 deletions(-) -- 2.54.0

1 month, 1 week

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[PATCH] Documentation: Extend the real-time hardware bits with some firmware bits

by Sebastian Andrzej Siewior

I have been reviewing how OP‑TEE is implemented and how secure‑world invocations behave. The goal was to determine whether an OP‑TEE call can delay the Linux side and introduce latency depending on the time spent in the secure world. Similar latency effects are already known for EFI runtime services, but this was not documented. To mitigate the impact, EFI runtime invocations can be restricted to specific CPUs so that real‑time workloads on other CPUs remain unaffected. This mechanism, however, is only described in the commit that introduced it. This change adds a firmware section that documents these behaviours explicitly. It highlights cases where firmware can delay the kernel, information that may be unfamiliar to some users and surprising-or concerning-to others. Assisted-by: Microsoft-Copilot Signed-off-by: Sebastian Andrzej Siewior <bigeasy(a)linutronix.de> --- I would appreciate an ACK from the OP-TEE camp that I got my little research right. Documentation/core-api/real-time/hardware.rst | 92 +++++++++++++++++++ 1 file changed, 92 insertions(+) diff --git a/Documentation/core-api/real-time/hardware.rst b/Documentation/core-api/real-time/hardware.rst index 19f9bb3786e03..fb113848c2f70 100644 --- a/Documentation/core-api/real-time/hardware.rst +++ b/Documentation/core-api/real-time/hardware.rst @@ -130,3 +130,95 @@ https://github.com/Linutronix/RTC-Testbench. The goal of this project is to validate real-time network communication. It can be thought of as a "cyclictest" for networking and also serves as a starting point for application development. + +Firmware +-------- + +The firmware often plays a significant role in system operation because it can +perform tasks that the kernel cannot directly access, and in some cases it can +even preempt or intercept the kernel. + +A common example of firmware assisting the kernel is when it provides a generic +interface to a resource. Instead of accessing an RTC chip through an I2C host +controller, the kernel may query the firmware for the current time, and the +firmware then accesses the RTC behind the scenes. + +Firmware can also intercept kernel execution by providing services that +temporarily take control of the system. One example is memory scrubbing, where +the firmware periodically pauses the kernel, reads back portions of system +memory, and then returns control. During this time, the kernel is effectively +interrupted. +In contrast, some systems provide hardware‑based memory scrubbing, which +operates independently of firmware or software. See +Documentation/edac/scrub.rst for details. + +If the kernel is intercepted for longer periods then these periods can be made +visible with the hardware latency detector. See +Documentation/trace/hwlat_detector.rst. + +The kernel can also be intercepted in response to specific events, such as +overheating. In this case, the firmware may throttle the CPU or shut it down +immediately to prevent hardware damage. + +Unless the firmware is well documented, it should be thoroughly tested to +uncover any unexpected behaviour. + +EFI +~~~~ + +EFI provides runtime services that act as a communication interface between the +firmware and the operating system. One such service is reading and writing EFI +variables, which are used, for example, to determine the boot source. + +Invoking a runtime service may require the architecture to disable kernel +preemption or interrupts during the call. This means the duration of a service +invocation directly affects the system’s observable latency. There is also +nothing that prevents a service call from disabling interrupts internally while +it runs. + +For these reasons, EFI runtime services are disabled by default on a PREEMPT_RT +kernel. They can still be enabled at boot time or via a Kconfig option if +required. +The native EFI runtime service implementation (where both the EFI service and +the kernel are either 32‑bit or 64‑bit executables) uses a wrapper mechanism +that invokes the service through a dedicated workqueue. This workqueue is named +efi_runtime, and it can be restricted to a housekeeping CPU using the +``/sys/devices/virtual/workqueue/efi_runtime/cpumask`` sysfs file. Assigning it +to a housekeeping CPU ensures that potentially long service invocations do not +impact the real‑time workload which is restricted to other CPUs. + +It must also be verified that the runtime services behave as expected. Some +implementations on the x86 architecture pause all other CPUs while one CPU +performs the service call. In such cases, the interruption affects all CPUs, +and restricting the workqueue to a single CPU provides no benefit. + +OP-TEE (ARM) +~~~~~~~~~~~~ + +OP‑TEE uses a global serialization mechanism (the "big lock"), ensuring that on +each core only one OP‑TEE thread executes secure‑world code at a time. + +Execution flows from the normal world (Linux) into the secure world (OP‑TEE) +through the secure monitor at EL3. Linux and OP‑TEE cannot disable or mask each +other’s interrupts because both run at EL1 in different security states. + +Architecturally, the secure monitor can mask or reroute normal‑world interrupts +before entering the secure world. In a correct OP‑TEE/ TF‑A implementation, it +does not do this for the duration of secure calls. Normal‑world interrupts +remain deliverable, and a normal‑world IRQ will preempt OP‑TEE via EL3 and +return control to Linux. + +Secure‑world interrupts (FIQs) are possible if the SoC routes a device's +interrupt as secure. Such a secure FIQ will preempt Linux immediately, trap +into EL3, and transfer control to OP‑TEE's secure interrupt handler. Linux +cannot mask or preempt this. Secure FIQ handlers must therefore be extremely +short to avoid introducing noticeable latency. + +The transition from normal world -> secure monitor -> OP‑TEE and back introduces +additional latency due to world switching and context save/ restore. This +overhead is typically a few microseconds and usually remains in the noise +floor. + +If the secure monitor masks normal‑world interrupts during OP‑TEE invocations, +or if OP‑TEE uses long‑running secure FIQ handlers, then OP‑TEE can introduce +measurable latency spikes. -- 2.53.0

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