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/debugfs-driver-dcc | 127 +++++++++++++++++++++++++++ 1 file changed, 127 insertions(+) create mode 100644 Documentation/ABI/testing/debugfs-driver-dcc (limited to 'Documentation/ABI/testing/debugfs-driver-dcc') diff --git a/Documentation/ABI/testing/debugfs-driver-dcc b/Documentation/ABI/testing/debugfs-driver-dcc new file mode 100644 index 000000000..27ed5919d --- /dev/null +++ b/Documentation/ABI/testing/debugfs-driver-dcc @@ -0,0 +1,127 @@ +What: /sys/kernel/debug/dcc/.../ready +Date: December 2022 +Contact: Souradeep Chowdhury +Description: + This file is used to check the status of the dcc + hardware if it's ready to receive user configurations. + A 'Y' here indicates dcc is ready. + +What: /sys/kernel/debug/dcc/.../trigger +Date: December 2022 +Contact: Souradeep Chowdhury +Description: + This is the debugfs interface for manual software + triggers. The trigger can be invoked by writing '1' + to the file. + +What: /sys/kernel/debug/dcc/.../config_reset +Date: December 2022 +Contact: Souradeep Chowdhury +Description: + This file is used to reset the configuration of + a dcc driver to the default configuration. When '1' + is written to the file, all the previous addresses + stored in the driver gets removed and users need to + reconfigure addresses again. + +What: /sys/kernel/debug/dcc/.../[list-number]/config +Date: December 2022 +Contact: Souradeep Chowdhury +Description: + This stores the addresses of the registers which + can be read in case of a hardware crash or manual + software triggers. The input addresses type + can be one of following dcc instructions: read, + write, read-write, and loop type. The lists need to + be configured sequentially and not in a overlapping + manner; e.g. users can jump to list x only after + list y is configured and enabled. The input format for + each type is as follows: + + i) Read instruction + + :: + + echo R >/sys/kernel/debug/dcc/../[list-number]/config + + where: + + + The address to be read. + + + The addresses word count, starting from address <1>. + Each word is 32 bits (4 bytes). If omitted, defaulted + to 1. + + + The bus type, which can be either 'apb' or 'ahb'. + The default is 'ahb' if leaved out. + + ii) Write instruction + + :: + + echo W > /sys/kernel/debug/dcc/../[list-number]/config + + where: + + + The address to be written. + + + The value to be written at . + + + The bus type, which can be either 'apb' or 'ahb'. + + iii) Read-write instruction + + :: + + echo RW > /sys/kernel/debug/dcc/../[list-number]/config + + where: + + + The address to be read and written. + + + The value to be written at . + + + The value mask. + + iv) Loop instruction + + :: + + echo L
... > /sys/kernel/debug/dcc/../[list-number]/config + + where: + + + Number of iterations + +
+ total number of addresses to be written + +
+ Space-separated list of addresses. + +What: /sys/kernel/debug/dcc/.../[list-number]/enable +Date: December 2022 +Contact: Souradeep Chowdhury +Description: + This debugfs interface is used for enabling the + the dcc hardware. A file named "enable" is in the + directory list number where users can enable/disable + the specific list by writing boolean (1 or 0) to the + file. + + On enabling the dcc, all the addresses specified + by the user for the corresponding list is written + into dcc sram which is read by the dcc hardware + on manual or crash induced triggers. Lists must + be configured and enabled sequentially, e.g. list + 2 can only be enabled when list 1 have so. -- cgit v1.3.1