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, 100 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/technisat.rst b/Documentation/admin-guide/media/technisat.rst
new file mode 100644
index 000000000..9eaa12366
--- /dev/null
+++ b/Documentation/admin-guide/media/technisat.rst
@@ -0,0 +1,100 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+How to set up the Technisat/B2C2 Flexcop devices
+================================================
+
+.. note::
+
+   This documentation is outdated.
+
+Author: Uwe Bugla <uwe.bugla@gmx.de> August 2009
+
+Find out what device you have
+-----------------------------
+
+Important Notice: The driver does NOT support Technisat USB 2 devices!
+
+First start your linux box with a shipped kernel:
+
+.. code-block:: none
+
+	lspci -vvv for a PCI device (lsusb -vvv for an USB device) will show you for example:
+	02:0b.0 Network controller: Techsan Electronics Co Ltd B2C2 FlexCopII DVB chip /
+	Technisat SkyStar2 DVB card (rev 02)
+
+	dmesg | grep frontend may show you for example:
+	DVB: registering frontend 0 (Conexant CX24123/CX24109)...
+
+Kernel compilation:
+-------------------
+
+If the Flexcop / Technisat is the only DVB / TV / Radio device in your box
+get rid of unnecessary modules and check this one:
+
+``Multimedia support`` => ``Customise analog and hybrid tuner modules to build``
+
+In this directory uncheck every driver which is activated there
+(except ``Simple tuner support`` for ATSC 3rd generation only -> see case 9 please).
+
+Then please activate:
+
+- Main module part:
+
+  ``Multimedia support`` => ``DVB/ATSC adapters`` => ``Technisat/B2C2 FlexcopII(b) and FlexCopIII adapters``
+
+  #) => ``Technisat/B2C2 Air/Sky/Cable2PC PCI`` (PCI card) or
+  #) => ``Technisat/B2C2 Air/Sky/Cable2PC USB`` (USB 1.1 adapter)
+     and for troubleshooting purposes:
+  #) => ``Enable debug for the B2C2 FlexCop drivers``
+
+- Frontend / Tuner / Demodulator module part:
+
+  ``Multimedia support`` => ``DVB/ATSC adapters``
+   => ``Customise the frontend modules to build`` ``Customise DVB frontends`` =>
+
+  - SkyStar DVB-S Revision 2.3:
+
+    #) => ``Zarlink VP310/MT312/ZL10313 based``
+    #) => ``Generic I2C PLL based tuners``
+
+  - SkyStar DVB-S Revision 2.6:
+
+    #) => ``ST STV0299 based``
+    #) => ``Generic I2C PLL based tuners``
+
+  - SkyStar DVB-S Revision 2.7:
+
+    #) => ``Samsung S5H1420 based``
+    #) => ``Integrant ITD1000 Zero IF tuner for DVB-S/DSS``
+    #) => ``ISL6421 SEC controller``
+
+  - SkyStar DVB-S Revision 2.8:
+
+    #) => ``Conexant CX24123 based``
+    #) => ``Conexant CX24113/CX24128 tuner for DVB-S/DSS``
+    #) => ``ISL6421 SEC controller``
+
+  - AirStar DVB-T card:
+
+    #) => ``Zarlink MT352 based``
+    #) => ``Generic I2C PLL based tuners``
+
+  - CableStar DVB-C card:
+
+    #) => ``ST STV0297 based``
+    #) => ``Generic I2C PLL based tuners``
+
+  - AirStar ATSC card 1st generation:
+
+    #) => ``Broadcom BCM3510``
+
+  - AirStar ATSC card 2nd generation:
+
+    #) => ``NxtWave Communications NXT2002/NXT2004 based``
+    #) => ``Generic I2C PLL based tuners``
+
+  - AirStar ATSC card 3rd generation:
+
+    #) => ``LG Electronics LGDT3302/LGDT3303 based``
+    #) ``Multimedia support`` => ``Customise analog and hybrid tuner modules to build`` => ``Simple tuner support``
+