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, 46 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-fsi b/Documentation/ABI/testing/sysfs-bus-fsi
new file mode 100644
index 000000000..76e0caa0c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-fsi
@@ -0,0 +1,46 @@
+What:           /sys/bus/platform/devices/../fsi-master/fsi0/rescan
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        linux-fsi@lists.ozlabs.org
+Description:
+                Initiates a FSI master scan for all connected slave devices
+		on its links.
+
+What:           /sys/bus/platform/devices/../fsi-master/fsi0/break
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        linux-fsi@lists.ozlabs.org
+Description:
+		Sends an FSI BREAK command on a master's communication
+		link to any connected slaves.  A BREAK resets connected
+		device's logic and preps it to receive further commands
+		from the master.
+
+What:           /sys/bus/platform/devices/../fsi-master/fsi0/slave@00:00/term
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        linux-fsi@lists.ozlabs.org
+Description:
+		Sends an FSI terminate command from the master to its
+		connected slave. A terminate resets the slave's state machines
+		that control access to the internally connected engines.  In
+		addition the slave freezes its internal error register for
+		debugging purposes.  This command is also needed to abort any
+		ongoing operation in case of an expired 'Master Time Out'
+		timer.
+
+What:           /sys/bus/platform/devices/../fsi-master/fsi0/slave@00:00/raw
+Date:		May 2017
+KernelVersion:  4.12
+Contact:        linux-fsi@lists.ozlabs.org
+Description:
+		Provides a means of reading/writing a 32 bit value from/to a
+		specified FSI bus address.
+
+What:           /sys/bus/platform/devices/../cfam_reset
+Date:		Sept 2020
+KernelVersion:  5.10
+Contact:        linux-fsi@lists.ozlabs.org
+Description:
+		Provides a means of resetting the cfam that is attached to the
+		FSI device.