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/drivers/tty/serial/timbuart.h b/drivers/tty/serial/timbuart.h
new file mode 100644
index 000000000..007e59af6
--- /dev/null
+++ b/drivers/tty/serial/timbuart.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * timbuart.c timberdale FPGA GPIO driver
+ * Copyright (c) 2009 Intel Corporation
+ */
+
+/* Supports:
+ * Timberdale FPGA UART
+ */
+
+#ifndef _TIMBUART_H
+#define _TIMBUART_H
+
+#define TIMBUART_FIFO_SIZE	2048
+
+#define TIMBUART_RXFIFO		0x08
+#define TIMBUART_TXFIFO		0x0c
+#define TIMBUART_IER		0x10
+#define TIMBUART_IPR		0x14
+#define TIMBUART_ISR		0x18
+#define TIMBUART_CTRL		0x1c
+#define TIMBUART_BAUDRATE	0x20
+
+#define TIMBUART_CTRL_RTS	0x01
+#define TIMBUART_CTRL_CTS	0x02
+#define TIMBUART_CTRL_FLSHTX	0x40
+#define TIMBUART_CTRL_FLSHRX	0x80
+
+#define TXBF		0x01
+#define TXBAE		0x02
+#define CTS_DELTA	0x04
+#define RXDP		0x08
+#define RXBAF		0x10
+#define RXBF		0x20
+#define RXTT		0x40
+#define RXBNAE		0x80
+#define TXBE		0x100
+
+#define RXFLAGS (RXDP | RXBAF | RXBF | RXTT | RXBNAE)
+#define TXFLAGS (TXBF | TXBAE)
+
+#define TIMBUART_MAJOR 204
+#define TIMBUART_MINOR 192
+
+#endif /* _TIMBUART_H */
+