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-genwqe | 91 +++++++++++++++++++++++++ 1 file changed, 91 insertions(+) create mode 100644 Documentation/ABI/testing/debugfs-driver-genwqe (limited to 'Documentation/ABI/testing/debugfs-driver-genwqe') diff --git a/Documentation/ABI/testing/debugfs-driver-genwqe b/Documentation/ABI/testing/debugfs-driver-genwqe new file mode 100644 index 000000000..b45b01654 --- /dev/null +++ b/Documentation/ABI/testing/debugfs-driver-genwqe @@ -0,0 +1,91 @@ +What: /sys/kernel/debug/genwqe/genwqe_card/ddcb_info +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: DDCB queue dump used for debugging queueing problems. + +What: /sys/kernel/debug/genwqe/genwqe_card/curr_regs +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Dump of the current error registers. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/curr_dbg_uid0 +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Internal chip state of UID0 (unit id 0). + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/curr_dbg_uid1 +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Internal chip state of UID1. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/curr_dbg_uid2 +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Internal chip state of UID2. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/prev_regs +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Dump of the error registers before the last reset of + the card occurred. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/prev_dbg_uid0 +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Internal chip state of UID0 before card was reset. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/prev_dbg_uid1 +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Internal chip state of UID1 before card was reset. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/prev_dbg_uid2 +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Internal chip state of UID2 before card was reset. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/info +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Comprehensive summary of bitstream version and software + version. Used bitstream and bitstream clocking information. + +What: /sys/kernel/debug/genwqe/genwqe_card/err_inject +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Possibility to inject error cases to ensure that the drivers + error handling code works well. + +What: /sys/kernel/debug/genwqe/genwqe_card/vf<0..14>_jobtimeout_msec +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Default VF timeout 250ms. Testing might require 1000ms. + Using 0 will use the cards default value (whatever that is). + + The timeout depends on the max number of available cards + in the system and the maximum allowed queue size. + + The driver ensures that the settings are done just before + the VFs get enabled. Changing the timeouts in flight is not + possible. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/jobtimer +Date: Oct 2013 +Contact: haver@linux.vnet.ibm.com +Description: Dump job timeout register values for PF and VFs. + Only available for PF. + +What: /sys/kernel/debug/genwqe/genwqe_card/queue_working_time +Date: Dec 2013 +Contact: haver@linux.vnet.ibm.com +Description: Dump queue working time register values for PF and VFs. + Only available for PF. -- cgit v1.3.1