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, 98 insertions, 0 deletions

diff --git a/Documentation/gpu/msm-crash-dump.rst b/Documentation/gpu/msm-crash-dump.rst
new file mode 100644
index 000000000..9509cc422
--- /dev/null
+++ b/Documentation/gpu/msm-crash-dump.rst
@@ -0,0 +1,98 @@
+:orphan:
+
+=====================
+MSM Crash Dump Format
+=====================
+
+Following a GPU hang the MSM driver outputs debugging information via
+/sys/kernel/dri/X/show or via devcoredump (/sys/class/devcoredump/dcdX/data).
+This document describes how the output is formatted.
+
+Each entry is in the form key: value. Sections headers will not have a value
+and all the contents of a section will be indented two spaces from the header.
+Each section might have multiple array entries the start of which is designated
+by a (-).
+
+Mappings
+--------
+
+kernel
+	The kernel version that generated the dump (UTS_RELEASE).
+
+module
+	The module that generated the crashdump.
+
+time
+	The kernel time at crash formatted as seconds.microseconds.
+
+comm
+	Comm string for the binary that generated the fault.
+
+cmdline
+	Command line for the binary that generated the fault.
+
+revision
+	ID of the GPU that generated the crash formatted as
+	core.major.minor.patchlevel separated by dots.
+
+rbbm-status
+	The current value of RBBM_STATUS which shows what top level GPU
+	components are in use at the time of crash.
+
+ringbuffer
+	Section containing the contents of each ringbuffer. Each ringbuffer is
+	identified with an id number.
+
+	id
+		Ringbuffer ID (0 based index).  Each ringbuffer in the section
+		will have its own unique id.
+	iova
+		GPU address of the ringbuffer.
+
+	last-fence
+		The last fence that was issued on the ringbuffer
+
+	retired-fence
+		The last fence retired on the ringbuffer.
+
+	rptr
+		The current read pointer (rptr) for the ringbuffer.
+
+	wptr
+		The current write pointer (wptr) for the ringbuffer.
+
+	size
+		Maximum size of the ringbuffer programmed in the hardware.
+
+	data
+		The contents of the ring encoded as ascii85.  Only the used
+		portions of the ring will be printed.
+
+bo
+	List of buffers from the hanging submission if available.
+	Each buffer object will have a uinque iova.
+
+	iova
+		GPU address of the buffer object.
+
+	size
+		Allocated size of the buffer object.
+
+	data
+		The contents of the buffer object encoded with ascii85.  Only
+		Trailing zeros at the end of the buffer will be skipped.
+
+registers
+	Set of registers values. Each entry is on its own line enclosed
+	by brackets { }.
+
+	offset
+		Byte offset of the register from the start of the
+		GPU memory region.
+
+	value
+		Hexadecimal value of the register.
+
+registers-hlsq
+		(5xx only) Register values from the HLSQ aperture.
+		Same format as the register section.