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/process/maintainer-devicetree.rst | 72 +++++++++++++++++++++++++ 1 file changed, 72 insertions(+) create mode 100644 Documentation/process/maintainer-devicetree.rst (limited to 'Documentation/process/maintainer-devicetree.rst') diff --git a/Documentation/process/maintainer-devicetree.rst b/Documentation/process/maintainer-devicetree.rst new file mode 100644 index 000000000..ecc3ed638 --- /dev/null +++ b/Documentation/process/maintainer-devicetree.rst @@ -0,0 +1,72 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================================== +Devicetree and Open Firmware Subsystem +====================================== + +Other Process Documents +----------------------- + +Please see the documents in Documentation/devicetree/bindings/ for information +on how to write proper Devicetree bindings and how to submit patches. + +Patch Review and Handling +------------------------- + +Patches handled by Devicetree maintainers are processed differently depending +on the patch type: + +1. Core OF driver code, e.g. drivers/of/: + patches are reviewed and applied by DT maintainers. + +2. Devicetree bindings: + patches are reviewed by DT maintainers, but should be applied by subsystem + maintainers except in certain cases. See also *For kernel maintainers* in + Documentation/devicetree/bindings/submitting-patches.rst. + +3. DTS and drivers: + DT maintainers might provide comments, but review is generally not expected. + DTS must pass schema checks (dtbs_check) or at least do not add any + new warnings. + +Patchwork +~~~~~~~~~ + +Devicetree maintainers review patches using Patchwork, so the current status of +a patch can be checked there. For typical driver submissions, Patchwork +receives the entire patch set, but only a few patches are usually Devicetree +bindings that are reviewed by DT maintainers. + +Explanation of Patchwork statuses: + + - **New**: Not yet processed by the automation toolset. + - **Needs ACK**: Waiting for review by DT maintainers. + - **Handled Elsewhere**: Non-DT patch; not being reviewed here. + - **RFC**: Patch was likely ignored because it was an incomplete RFC. + - **Changes Requested**: Patch was reviewed and DT maintainers expect changes. + - **Accepted**: Patch was reviewed and applied by DT maintainers to their tree. + - **Not Applicable**: Patch was reviewed and is likely in good shape, with a + *Reviewed-by* or *Acked-by* tag provided, but DT maintainers expect someone + else to apply it. + +Patch Re-review and Pinging +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Due to the high volume of email traffic, Devicetree maintainers do not read +every email they receive and instead rely on Patchwork during the review +process. They also often skip patches that have already been reviewed. + +As a result, maintainers might miss: + +1. Questions about already reviewed patches. +2. Pings, for example when a patch has been reviewed by DT maintainers but has + not been picked up by subsystem maintainers. + +Such cases can be addressed by: + +1. Pinging DT maintainers on the IRC channel. +2. Dropping the DT maintainer’s *Acked-by* or *Reviewed-by* tag when sending a new + version of the patch set, together with an explanation in the patch + changelog describing why the tag was removed and what is expected from DT + maintainers. + -- cgit v1.3.1