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-amd-iommu | 131 ++++++++++++++++++++++++++++ 1 file changed, 131 insertions(+) create mode 100644 Documentation/ABI/testing/debugfs-amd-iommu (limited to 'Documentation/ABI/testing/debugfs-amd-iommu') diff --git a/Documentation/ABI/testing/debugfs-amd-iommu b/Documentation/ABI/testing/debugfs-amd-iommu new file mode 100644 index 000000000..5621a66aa --- /dev/null +++ b/Documentation/ABI/testing/debugfs-amd-iommu @@ -0,0 +1,131 @@ +What: /sys/kernel/debug/iommu/amd/iommu/mmio +Date: January 2025 +Contact: Dheeraj Kumar Srivastava +Description: + This file provides read/write access for user input. Users specify the + MMIO register offset for iommu, and the file outputs the corresponding + MMIO register value of iommu + + Example:: + + $ echo "0x18" > /sys/kernel/debug/iommu/amd/iommu00/mmio + $ cat /sys/kernel/debug/iommu/amd/iommu00/mmio + + Output:: + + Offset:0x18 Value:0x000c22000003f48d + +What: /sys/kernel/debug/iommu/amd/iommu/capability +Date: January 2025 +Contact: Dheeraj Kumar Srivastava +Description: + This file provides read/write access for user input. Users specify the + capability register offset for iommu, and the file outputs the + corresponding capability register value of iommu. + + Example:: + + $ echo "0x10" > /sys/kernel/debug/iommu/amd/iommu00/capability + $ cat /sys/kernel/debug/iommu/amd/iommu00/capability + + Output:: + + Offset:0x10 Value:0x00203040 + +What: /sys/kernel/debug/iommu/amd/iommu/cmdbuf +Date: January 2025 +Contact: Dheeraj Kumar Srivastava +Description: + This file is a read-only output file containing iommu command + buffer entries. + + Examples:: + + $ cat /sys/kernel/debug/iommu/amd/iommu/cmdbuf + + Output:: + + CMD Buffer Head Offset:339 Tail Offset:339 + 0: 00835001 10000001 00003c00 00000000 + 1: 00000000 30000005 fffff003 7fffffff + 2: 00835001 10000001 00003c01 00000000 + 3: 00000000 30000005 fffff003 7fffffff + 4: 00835001 10000001 00003c02 00000000 + 5: 00000000 30000005 fffff003 7fffffff + 6: 00835001 10000001 00003c03 00000000 + 7: 00000000 30000005 fffff003 7fffffff + 8: 00835001 10000001 00003c04 00000000 + 9: 00000000 30000005 fffff003 7fffffff + 10: 00835001 10000001 00003c05 00000000 + 11: 00000000 30000005 fffff003 7fffffff + [...] + +What: /sys/kernel/debug/iommu/amd/devid +Date: January 2025 +Contact: Dheeraj Kumar Srivastava +Description: + This file provides read/write access for user input. Users specify the + device ID, which can be used to dump IOMMU data structures such as the + interrupt remapping table and device table. + + Example: + + 1. + :: + + $ echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid + $ cat /sys/kernel/debug/iommu/amd/devid + + Output:: + + 0000:01:00.0 + + 2. + :: + + $ echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid + $ cat /sys/kernel/debug/iommu/amd/devid + + Output:: + + 0000:01:00.0 + +What: /sys/kernel/debug/iommu/amd/devtbl +Date: January 2025 +Contact: Dheeraj Kumar Srivastava +Description: + This file is a read-only output file containing the device table entry + for the device ID provided in /sys/kernel/debug/iommu/amd/devid. + + Example:: + + $ cat /sys/kernel/debug/iommu/amd/devtbl + + Output:: + + DeviceId QWORD[3] QWORD[2] QWORD[1] QWORD[0] iommu + 0000:01:00.0 0000000000000000 20000001373b8013 0000000000000038 6000000114d7b603 iommu3 + +What: /sys/kernel/debug/iommu/amd/irqtbl +Date: January 2025 +Contact: Dheeraj Kumar Srivastava +Description: + This file is a read-only output file containing valid IRT table entries + for the device ID provided in /sys/kernel/debug/iommu/amd/devid. + + Example:: + + $ cat /sys/kernel/debug/iommu/amd/irqtbl + + Output:: + + DeviceId 0000:01:00.0 + IRT[0000] 0000000000000020 0000000000000241 + IRT[0001] 0000000000000020 0000000000000841 + IRT[0002] 0000000000000020 0000000000002041 + IRT[0003] 0000000000000020 0000000000008041 + IRT[0004] 0000000000000020 0000000000020041 + IRT[0005] 0000000000000020 0000000000080041 + IRT[0006] 0000000000000020 0000000000200041 + IRT[0007] 0000000000000020 0000000000800041 + [...] -- cgit v1.3.1