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, 163 insertions, 0 deletions

diff --git a/Documentation/process/kernel-enforcement-statement.rst b/Documentation/process/kernel-enforcement-statement.rst
new file mode 100644
index 000000000..dc2d813b2
--- /dev/null
+++ b/Documentation/process/kernel-enforcement-statement.rst
@@ -0,0 +1,163 @@
+.. _process_statement_kernel:
+
+Linux Kernel Enforcement Statement
+----------------------------------
+
+As developers of the Linux kernel, we have a keen interest in how our software
+is used and how the license for our software is enforced.  Compliance with the
+reciprocal sharing obligations of GPL-2.0 is critical to the long-term
+sustainability of our software and community.
+
+Although there is a right to enforce the separate copyright interests in the
+contributions made to our community, we share an interest in ensuring that
+individual enforcement actions are conducted in a manner that benefits our
+community and do not have an unintended negative impact on the health and
+growth of our software ecosystem.  In order to deter unhelpful enforcement
+actions, we agree that it is in the best interests of our development
+community to undertake the following commitment to users of the Linux kernel
+on behalf of ourselves and any successors to our copyright interests:
+
+    Notwithstanding the termination provisions of the GPL-2.0, we agree that
+    it is in the best interests of our development community to adopt the
+    following provisions of GPL-3.0 as additional permissions under our
+    license with respect to any non-defensive assertion of rights under the
+    license.
+
+	However, if you cease all violation of this License, then your license
+	from a particular copyright holder is reinstated (a) provisionally,
+	unless and until the copyright holder explicitly and finally
+	terminates your license, and (b) permanently, if the copyright holder
+	fails to notify you of the violation by some reasonable means prior to
+	60 days after the cessation.
+
+	Moreover, your license from a particular copyright holder is
+	reinstated permanently if the copyright holder notifies you of the
+	violation by some reasonable means, this is the first time you have
+	received notice of violation of this License (for any work) from that
+	copyright holder, and you cure the violation prior to 30 days after
+	your receipt of the notice.
+
+Our intent in providing these assurances is to encourage more use of the
+software.  We want companies and individuals to use, modify and distribute
+this software.  We want to work with users in an open and transparent way to
+eliminate any uncertainty about our expectations regarding compliance or
+enforcement that might limit adoption of our software.  We view legal action
+as a last resort, to be initiated only when other community efforts have
+failed to resolve the problem.
+
+Finally, once a non-compliance issue is resolved, we hope the user will feel
+welcome to join us in our efforts on this project.  Working together, we will
+be stronger.
+
+Except where noted below, we speak only for ourselves, and not for any company
+we might work for today, have in the past, or will in the future.
+
+  - Laura Abbott
+  - Bjorn Andersson (Linaro)
+  - Andrea Arcangeli
+  - Neil Armstrong
+  - Jens Axboe
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+  - Khalid Aziz
+  - Ralf Baechle
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+  - Tim Bird
+  - Paolo Bonzini
+  - Christian Borntraeger
+  - Mark Brown (Linaro)
+  - Paul Burton
+  - Javier Martinez Canillas
+  - Rob Clark
+  - Kees Cook (Google)
+  - Jonathan Corbet
+  - Dennis Dalessandro
+  - Vivien Didelot (Savoir-faire Linux)
+  - Hans de Goede
+  - Mel Gorman (SUSE)
+  - Sven Eckelmann
+  - Alex Elder (Linaro)
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+  - Bhumika Goyal
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