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-bus-cdx | 121 ++++++++++++++++++++++++++++++++ 1 file changed, 121 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-bus-cdx (limited to 'Documentation/ABI/testing/sysfs-bus-cdx') diff --git a/Documentation/ABI/testing/sysfs-bus-cdx b/Documentation/ABI/testing/sysfs-bus-cdx new file mode 100644 index 000000000..e84277531 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-bus-cdx @@ -0,0 +1,121 @@ +What: /sys/bus/cdx/rescan +Date: March 2023 +Contact: nipun.gupta@amd.com +Description: + Writing y/1/on to this file will cause rescan of the bus + and devices on the CDX bus. Any new devices are scanned and + added to the list of Linux devices and any devices removed are + also deleted from Linux. + + For example:: + + # echo 1 > /sys/bus/cdx/rescan + +What: /sys/bus/cdx/devices/.../vendor +Date: March 2023 +Contact: nipun.gupta@amd.com +Description: + Vendor ID for this CDX device, in hexadecimal. Vendor ID is + 16 bit identifier which is specific to the device manufacturer. + Combination of Vendor ID and Device ID identifies a device. + +What: /sys/bus/cdx/devices/.../device +Date: March 2023 +Contact: nipun.gupta@amd.com +Description: + Device ID for this CDX device, in hexadecimal. Device ID is + 16 bit identifier to identify a device type within the range + of a device manufacturer. + Combination of Vendor ID and Device ID identifies a device. + +What: /sys/bus/cdx/devices/.../subsystem_vendor +Date: July 2023 +Contact: puneet.gupta@amd.com +Description: + Subsystem Vendor ID for this CDX device, in hexadecimal. + Subsystem Vendor ID is 16 bit identifier specific to the + card manufacturer. + +What: /sys/bus/cdx/devices/.../subsystem_device +Date: July 2023 +Contact: puneet.gupta@amd.com +Description: + Subsystem Device ID for this CDX device, in hexadecimal + Subsystem Device ID is 16 bit identifier specific to the + card manufacturer. + +What: /sys/bus/cdx/devices/.../class +Date: July 2023 +Contact: puneet.gupta@amd.com +Description: + This file contains the class of the CDX device, in hexadecimal. + Class is 24 bit identifier specifies the functionality of the device. + +What: /sys/bus/cdx/devices/.../revision +Date: July 2023 +Contact: puneet.gupta@amd.com +Description: + This file contains the revision field of the CDX device, in hexadecimal. + Revision is 8 bit revision identifier of the device. + +What: /sys/bus/cdx/devices/.../enable +Date: October 2023 +Contact: abhijit.gangurde@amd.com +Description: + CDX bus should be disabled before updating the devices in FPGA. + Writing n/0/off will attempt to disable the CDX bus and. + writing y/1/on will attempt to enable the CDX bus. Reading this file + gives the current state of the bus, 1 for enabled and 0 for disabled. + + For example:: + + # echo 1 > /sys/bus/cdx/.../enable + +What: /sys/bus/cdx/devices/.../reset +Date: March 2023 +Contact: nipun.gupta@amd.com +Description: + Writing y/1/on to this file resets the CDX device or all devices + on the bus. On resetting the device, the corresponding driver is + notified twice, once before the device is being reset, and again + after the reset has been complete. + + For example:: + + # echo 1 > /sys/bus/cdx/.../reset + +What: /sys/bus/cdx/devices/.../remove +Date: March 2023 +Contact: tarak.reddy@amd.com +Description: + Writing y/1/on to this file removes the corresponding + device from the CDX bus. If the device is to be reconfigured + reconfigured in the Hardware, the device can be removed, so + that the device driver does not access the device while it is + being reconfigured. + + For example:: + + # echo 1 > /sys/bus/cdx/devices/.../remove + +What: /sys/bus/cdx/devices/.../resource +Date: July 2023 +Contact: puneet.gupta@amd.com +Description: + The resource binary file contains the content of the memory + regions. These files can be m'maped from userspace. + +What: /sys/bus/cdx/devices/.../modalias +Date: July 2023 +Contact: nipun.gupta@amd.com +Description: + This attribute indicates the CDX ID of the device. + That is in the format: + cdx:vXXXXdXXXXsvXXXXsdXXXXcXXXXXX, + where: + + - vXXXX contains the vendor ID; + - dXXXX contains the device ID; + - svXXXX contains the subsystem vendor ID; + - sdXXXX contains the subsystem device ID; + - cXXXXXX contains the device class. -- cgit v1.3.1