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, 202 insertions, 0 deletions

diff --git a/Documentation/driver-api/cxl/maturity-map.rst b/Documentation/driver-api/cxl/maturity-map.rst
new file mode 100644
index 000000000..282c1102d
--- /dev/null
+++ b/Documentation/driver-api/cxl/maturity-map.rst
@@ -0,0 +1,202 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. include:: <isonum.txt>
+
+===========================================
+Compute Express Link Subsystem Maturity Map
+===========================================
+
+The Linux CXL subsystem tracks the dynamic `CXL specification
+<https://computeexpresslink.org/cxl-specification-landing-page>`_ that
+continues to respond to new use cases with new features, capability
+updates and fixes. At any given point some aspects of the subsystem are
+more mature than others. While the periodic pull requests summarize the
+`work being incorporated each merge window
+<https://lore.kernel.org/linux-cxl/?q=s%3APULL+s%3ACXL+tc%3Atorvalds+NOT+s%3ARe>`_,
+those do not always convey progress relative to a starting point and a
+future end goal.
+
+What follows is a coarse breakdown of the subsystem's major
+responsibilities along with a maturity score. The expectation is that
+the change-history of this document provides an overview summary of the
+subsystem maturation over time.
+
+The maturity scores are:
+
+- [3] Mature: Work in this area is complete and no changes on the horizon.
+  Note that this score can regress from one kernel release to the next
+  based on new test results or end user reports.
+
+- [2] Stabilizing: Major functionality operational, common cases are
+  mature, but known corner cases are still a work in progress.
+
+- [1] Initial: Capability that has exited the Proof of Concept phase, but
+  may still have significant gaps to close and fixes to apply as real
+  world testing occurs.
+
+- [0] Known gap: Feature is on a medium to long term horizon to
+  implement.  If the specification has a feature that does not even have
+  a '0' score in this document, there is a good chance that no one in
+  the linux-cxl@vger.kernel.org community has started to look at it.
+
+- X: Out of scope for kernel enabling, or kernel enabling not required
+
+Feature and Capabilities
+========================
+
+Enumeration / Provisioning
+--------------------------
+All of the fundamental enumeration an object model of the subsystem is
+in place, but there are several corner cases that are pending closure.
+
+
+* [2] CXL Window Enumeration
+
+  * [2] :ref:`Extended-linear memory-side cache <extended-linear>`
+  * [0] Low Memory-hole
+  * [X] Hetero-interleave
+
+* [2] Switch Enumeration
+
+  * [0] CXL register enumeration link-up dependency
+
+* [2] HDM Decoder Configuration
+
+  * [0] Decoder target and granularity constraints
+
+* [2] Performance enumeration
+
+  * [3] Endpoint CDAT
+  * [3] Switch CDAT
+  * [1] CDAT to Core-mm integration
+
+    * [1] x86
+    * [0] Arm64
+    * [0] All other arch.
+
+  * [0] Shared link
+
+* [2] Hotplug
+  (see CXL Window Enumeration)
+
+  * [0] Handle Soft Reserved conflicts
+
+* [0] :ref:`RCH link status <rch-link-status>`
+* [0] Fabrics / G-FAM (chapter 7)
+* [0] Global Access Endpoint
+
+
+RAS
+---
+In many ways CXL can be seen as a standardization of what would normally
+be handled by custom EDAC drivers. The open development here is
+mainly caused by the enumeration corner cases above.
+
+* [3] Component events (OS)
+* [2] Component events (FFM)
+* [1] Endpoint protocol errors (OS)
+* [1] Endpoint protocol errors (FFM)
+* [0] Switch protocol errors (OS)
+* [1] Switch protocol errors (FFM)
+* [2] DPA->HPA Address translation
+
+    * [1] XOR Interleave translation
+      (see CXL Window Enumeration)
+
+* [1] Memory Failure coordination
+* [0] Scrub control
+* [2] ACPI error injection EINJ
+
+  * [0] EINJ v2
+  * [X] Compliance DOE
+
+* [2] Native error injection
+* [3] RCH error handling
+* [1] VH error handling
+* [0] PPR
+* [0] Sparing
+* [0] Device built in test
+
+
+Mailbox commands
+----------------
+
+* [3] Firmware update
+* [3] Health / Alerts
+* [1] :ref:`Background commands <background-commands>`
+* [3] Sanitization
+* [3] Security commands
+* [3] RAW Command Debug Passthrough
+* [0] CEL-only-validation Passthrough
+* [0] Switch CCI
+* [3] Timestamp
+* [1] PMEM labels
+* [3] PMEM GPF / Dirty Shutdown
+* [0] Scan Media
+
+PMU
+---
+* [1] Type 3 PMU
+* [0] Switch USP/ DSP, Root Port
+
+Security
+--------
+
+* [X] CXL Trusted Execution Environment Security Protocol (TSP)
+* [X] CXL IDE (subsumed by TSP)
+
+Memory-pooling
+--------------
+
+* [1] Hotplug of LDs (via PCI hotplug)
+* [0] Dynamic Capacity Device (DCD) Support
+
+Multi-host sharing
+------------------
+
+* [0] Hardware coherent shared memory
+* [0] Software managed coherency shared memory
+
+Multi-host memory
+-----------------
+
+* [0] Dynamic Capacity Device Support
+* [0] Sharing
+
+Accelerator
+-----------
+
+* [0] Accelerator memory enumeration HDM-D (CXL 1.1/2.0 Type-2)
+* [0] Accelerator memory enumeration HDM-DB (CXL 3.0 Type-2)
+* [0] CXL.cache 68b (CXL 2.0)
+* [0] CXL.cache 256b Cache IDs (CXL 3.0)
+
+User Flow Support
+-----------------
+
+* [2] Inject & clear poison by region offset
+
+Details
+=======
+
+.. _extended-linear:
+
+* **Extended-linear memory-side cache**: An HMAT proposal to enumerate the presence of a
+  memory-side cache where the cache capacity extends the SRAT address
+  range capacity. `See the ECN
+  <https://lore.kernel.org/linux-cxl/6650e4f835a0e_195e294a8@dwillia2-mobl3.amr.corp.intel.com.notmuch/>`_
+  for more details:
+
+.. _rch-link-status:
+
+* **RCH Link Status**: RCH (Restricted CXL Host) topologies, end up
+  hiding some standard registers like PCIe Link Status / Capabilities in
+  the CXL RCRB (Root Complex Register Block).
+
+.. _background-commands:
+
+* **Background commands**: The CXL background command mechanism is
+  awkward as the single slot is monopolized potentially indefinitely by
+  various commands. A `cancel on conflict
+  <http://lore.kernel.org/r/66035c2e8ba17_770232948b@dwillia2-xfh.jf.intel.com.notmuch>`_
+  facility is needed to make sure the kernel can ensure forward progress
+  of priority commands.