From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- Documentation/ABI/testing/sysfs-class-led | 89 +++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-led (limited to 'Documentation/ABI/testing/sysfs-class-led') diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led new file mode 100644 index 000000000..d4c918cc1 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-led @@ -0,0 +1,89 @@ +What: /sys/class/leds//brightness +Date: March 2006 +KernelVersion: 2.6.17 +Contact: Richard Purdie +Description: + Set the brightness of the LED. + + Most LEDs don't have hardware brightness support, so will + just be turned on for non-zero brightness settings. + + .. Note:: + + For multicolor LEDs, writing to this file will update all + LEDs within the group to a calculated percentage of what + each color LED intensity is set to. + + The percentage is calculated for each grouped LED via + the equation below:: + + led_brightness = brightness * multi_intensity/max_brightness + + For additional details please refer to + Documentation/leds/leds-class-multicolor.rst. + + The value is between 0 and /sys/class/leds//max_brightness + and is represented by as a decimal. + + Writing 0 to this file clears active trigger. + + Writing non-zero to this file while trigger is active changes the + top brightness trigger is going to use. + + + +What: /sys/class/leds//max_brightness +Date: March 2006 +KernelVersion: 2.6.17 +Contact: Richard Purdie +Description: + Maximum brightness level for this LED, default is 255 (LED_FULL). + + If the LED does not support different brightness levels, this + should be 1. + +What: /sys/class/leds//brightness_hw_changed +Date: January 2017 +KernelVersion: 4.11 +Description: + Last hardware set brightness level for this LED. Some LEDs + may be changed autonomously by hardware/firmware. Only LEDs + where this happens and the driver can detect this, will have + this file. + + This file supports poll() to detect when the hardware changes + the brightness. + + Reading this file will return the last brightness level set + by the hardware, this may be different from the current + brightness. Reading this file when no hw brightness change + event has happened will return an ENODATA error. + +What: /sys/class/leds//trigger +Date: March 2006 +KernelVersion: 2.6.17 +Contact: Richard Purdie +Description: + Set the trigger for this LED. A trigger is a kernel based source + of LED events. + + You can change triggers in a similar manner to the way an IO + scheduler is chosen. Trigger specific parameters can appear in + /sys/class/leds/ once a given trigger is selected. For + their documentation see `sysfs-class-led-trigger-*`. + + Writing "none" removes the trigger for this LED. + + Writing "default" sets the trigger to the LED's default trigger + (which would often be configured in the device tree for the + hardware). + +What: /sys/class/leds//inverted +Date: January 2011 +KernelVersion: 2.6.38 +Contact: Richard Purdie +Description: + Invert the LED on/off state. This parameter is specific to + gpio and backlight triggers. In case of the backlight trigger, + it is useful when driving a LED which is intended to indicate + a device in a standby like state. -- cgit v1.3.1