x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 166 insertions, 0 deletions

diff --git a/Documentation/tee/op-tee.rst b/Documentation/tee/op-tee.rst
new file mode 100644
index 000000000..b0ac097d5
--- /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.html