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, 42 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs b/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs
new file mode 100644
index 000000000..04ac62305
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs
@@ -0,0 +1,42 @@
+What:		/sys/bus/iio/devices/triggerX/trigger_now
+KernelVersion:	2.6.38
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This file is provided by the iio-trig-sysfs stand-alone trigger
+		driver. Writing this file with any value triggers an event
+		driven driver, associated with this trigger, to capture data
+		into an in kernel buffer. This approach can be valuable during
+		automated testing or in situations, where other trigger methods
+		are not applicable. For example no RTC or spare GPIOs.
+		X is the IIO index of the trigger.
+
+What:		/sys/bus/iio/devices/triggerX/name
+KernelVersion:	2.6.39
+Contact:	linux-iio@vger.kernel.org
+Description:
+		The name attribute holds a description string for the current
+		trigger. In order to associate the trigger with an IIO device
+		one should write this name string to
+		/sys/bus/iio/devices/iio:deviceY/trigger/current_trigger.
+
+What:		/sys/bus/iio/devices/iio_sysfs_trigger/add_trigger
+KernelVersion:	2.6.39
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This attribute is provided by the iio-trig-sysfs stand-alone
+		driver and it is used to activate the creation of a new trigger.
+		In order to achieve this, one should write a positive integer
+		into the associated file, which will serve as the id of the
+		trigger. If the trigger with the specified id is already present
+		in the system, an invalid argument message will be returned.
+
+What:		/sys/bus/iio/devices/iio_sysfs_trigger/remove_trigger
+KernelVersion:	2.6.39
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This attribute is used to unregister and delete a previously
+		created trigger from the list of available triggers. In order to
+		achieve this, one should write a positive integer into the
+		associated file, representing the id of the trigger that needs
+		to be removed. If the trigger can't be found, an invalid
+		argument message will be returned to the user.