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, 135 insertions, 0 deletions

diff --git a/Documentation/driver-api/s390-drivers.rst b/Documentation/driver-api/s390-drivers.rst
new file mode 100644
index 000000000..8c0845c4e
--- /dev/null
+++ b/Documentation/driver-api/s390-drivers.rst
@@ -0,0 +1,135 @@
+===================================
+Writing s390 channel device drivers
+===================================
+
+:Author: Cornelia Huck
+
+Introduction
+============
+
+This document describes the interfaces available for device drivers that
+drive s390 based channel attached I/O devices. This includes interfaces
+for interaction with the hardware and interfaces for interacting with
+the common driver core. Those interfaces are provided by the s390 common
+I/O layer.
+
+The document assumes a familarity with the technical terms associated
+with the s390 channel I/O architecture. For a description of this
+architecture, please refer to the "z/Architecture: Principles of
+Operation", IBM publication no. SA22-7832.
+
+While most I/O devices on a s390 system are typically driven through the
+channel I/O mechanism described here, there are various other methods
+(like the diag interface). These are out of the scope of this document.
+
+The s390 common I/O layer also provides access to some devices that are
+not strictly considered I/O devices. They are considered here as well,
+although they are not the focus of this document.
+
+Some additional information can also be found in the kernel source under
+Documentation/arch/s390/driver-model.rst.
+
+The css bus
+===========
+
+The css bus contains the subchannels available on the system. They fall
+into several categories:
+
+* Standard I/O subchannels, for use by the system. They have a child
+  device on the ccw bus and are described below.
+* I/O subchannels bound to the vfio-ccw driver. See
+  Documentation/arch/s390/vfio-ccw.rst.
+* Message subchannels. No Linux driver currently exists.
+* CHSC subchannels (at most one). The chsc subchannel driver can be used
+  to send asynchronous chsc commands.
+* eADM subchannels. Used for talking to storage class memory.
+
+The ccw bus
+===========
+
+The ccw bus typically contains the majority of devices available to a
+s390 system. Named after the channel command word (ccw), the basic
+command structure used to address its devices, the ccw bus contains
+so-called channel attached devices. They are addressed via I/O
+subchannels, visible on the css bus. A device driver for
+channel-attached devices, however, will never interact with the
+subchannel directly, but only via the I/O device on the ccw bus, the ccw
+device.
+
+I/O functions for channel-attached devices
+------------------------------------------
+
+Some hardware structures have been translated into C structures for use
+by the common I/O layer and device drivers. For more information on the
+hardware structures represented here, please consult the Principles of
+Operation.
+
+.. kernel-doc:: arch/s390/include/asm/cio.h
+   :internal:
+
+ccw devices
+-----------
+
+Devices that want to initiate channel I/O need to attach to the ccw bus.
+Interaction with the driver core is done via the common I/O layer, which
+provides the abstractions of ccw devices and ccw device drivers.
+
+The functions that initiate or terminate channel I/O all act upon a ccw
+device structure. Device drivers must not bypass those functions or
+strange side effects may happen.
+
+.. kernel-doc:: arch/s390/include/asm/ccwdev.h
+   :internal:
+
+.. kernel-doc:: drivers/s390/cio/device.c
+   :export:
+
+.. kernel-doc:: drivers/s390/cio/device_ops.c
+   :export:
+
+The channel-measurement facility
+--------------------------------
+
+The channel-measurement facility provides a means to collect measurement
+data which is made available by the channel subsystem for each channel
+attached device.
+
+.. kernel-doc:: arch/s390/include/uapi/asm/cmb.h
+   :internal:
+
+.. kernel-doc:: drivers/s390/cio/cmf.c
+   :export:
+
+The ccwgroup bus
+================
+
+The ccwgroup bus only contains artificial devices, created by the user.
+Many networking devices (e.g. qeth) are in fact composed of several ccw
+devices (like read, write and data channel for qeth). The ccwgroup bus
+provides a mechanism to create a meta-device which contains those ccw
+devices as slave devices and can be associated with the netdevice.
+
+ccw group devices
+-----------------
+
+.. kernel-doc:: arch/s390/include/asm/ccwgroup.h
+   :internal:
+
+.. kernel-doc:: drivers/s390/cio/ccwgroup.c
+   :export:
+
+Generic interfaces
+==================
+
+The following section contains interfaces in use not only by drivers
+dealing with ccw devices, but drivers for various other s390 hardware
+as well.
+
+Adapter interrupts
+------------------
+
+The common I/O layer provides helper functions for dealing with adapter
+interrupts and interrupt vectors.
+
+.. kernel-doc:: drivers/s390/cio/airq.c
+   :export: