x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

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) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 41 insertions, 0 deletions

diff --git a/Documentation/process/conclave.rst b/Documentation/process/conclave.rst
new file mode 100644
index 000000000..6a1234f54
--- /dev/null
+++ b/Documentation/process/conclave.rst
@@ -0,0 +1,41 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Linux kernel project continuity
+===============================
+
+The Linux kernel development project is widely distributed, with over
+100 maintainers each working to keep changes moving through their own
+repositories. The final step, though, is a centralized one where changes
+are pulled into the mainline repository. That is normally done by Linus
+Torvalds but, as was demonstrated by the 4.19 release in 2018, there are
+others who can do that work when the need arises.
+
+Should the maintainers of that repository become unwilling or unable to
+do that work going forward (including facilitating a transition), the
+project will need to find one or more replacements without delay. The
+process by which that will be done is listed below. $ORGANIZER is the
+last Maintainer Summit organizer or the current Linux Foundation (LF)
+Technical Advisory Board (TAB) Chair as a backup.
+
+- Within 72 hours, $ORGANIZER will open a discussion with the invitees
+  of the most recently concluded Maintainers Summit. A meeting of those
+  invitees and the TAB, either online or in-person, will be set as soon
+  as possible in a way that maximizes the number of people who can
+  participate.
+
+- If there has been no Maintainers Summit in the last 15 months, the set of
+  invitees for this meeting will be determined by the TAB.
+
+- The invitees to this meeting may bring in other maintainers as needed.
+
+- This meeting, chaired by $ORGANIZER, will consider options for the
+  ongoing management of the top-level kernel repository consistent with
+  the expectation that it maximizes the long term health of the project
+  and its community.
+
+- Within two weeks, a representative of this group will communicate to the
+  broader community, using the ksummit@lists.linux.dev mailing list, what
+  the next steps will be.
+
+The Linux Foundation, as guided by the TAB, will take the steps
+necessary to support and implement this plan.