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, 107 insertions, 0 deletions

diff --git a/drivers/auxdisplay/charlcd.h b/drivers/auxdisplay/charlcd.h
new file mode 100644
index 000000000..d10b89740
--- /dev/null
+++ b/drivers/auxdisplay/charlcd.h
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Character LCD driver for Linux
+ *
+ * Copyright (C) 2000-2008, Willy Tarreau <w@1wt.eu>
+ * Copyright (C) 2016-2017 Glider bvba
+ */
+
+#ifndef _CHARLCD_H
+#define _CHARLCD_H
+
+#define LCD_FLAG_B		0x0004	/* Blink on */
+#define LCD_FLAG_C		0x0008	/* Cursor on */
+#define LCD_FLAG_D		0x0010	/* Display on */
+#define LCD_FLAG_F		0x0020	/* Large font mode */
+#define LCD_FLAG_N		0x0040	/* 2-rows mode */
+#define LCD_FLAG_L		0x0080	/* Backlight enabled */
+
+enum charlcd_onoff {
+	CHARLCD_OFF = 0,
+	CHARLCD_ON,
+};
+
+enum charlcd_shift_dir {
+	CHARLCD_SHIFT_LEFT,
+	CHARLCD_SHIFT_RIGHT,
+};
+
+enum charlcd_fontsize {
+	CHARLCD_FONTSIZE_SMALL,
+	CHARLCD_FONTSIZE_LARGE,
+};
+
+enum charlcd_lines {
+	CHARLCD_LINES_1,
+	CHARLCD_LINES_2,
+};
+
+struct charlcd_ops;
+
+struct charlcd {
+	const struct charlcd_ops *ops;
+	const unsigned char *char_conv;	/* Optional */
+
+	int height;
+	int width;
+
+	/* Contains the LCD X and Y offset */
+	struct {
+		unsigned long x;
+		unsigned long y;
+	} addr;
+
+	void *drvdata;			/* Set by charlcd_alloc() */
+};
+
+/**
+ * struct charlcd_ops - Functions used by charlcd. Drivers have to implement
+ * these.
+ * @backlight: Turn backlight on or off. Optional.
+ * @print: Print one character to the display at current cursor position.
+ * The buffered cursor position is advanced by charlcd. The cursor should not
+ * wrap to the next line at the end of a line.
+ * @gotoxy: Set cursor to x, y. The x and y values to set the cursor to are
+ * previously set in addr.x and addr.y by charlcd.
+ * @home: Set cursor to 0, 0. The values in addr.x and addr.y are set to 0, 0 by
+ * charlcd prior to calling this function.
+ * @clear_display: Clear the whole display and set the cursor to 0, 0. The
+ * values in addr.x and addr.y are set to 0, 0 by charlcd after to calling this
+ * function.
+ * @init_display: Initialize the display.
+ * @shift_cursor: Shift cursor left or right one position.
+ * @shift_display: Shift whole display content left or right.
+ * @display: Turn display on or off.
+ * @cursor: Turn cursor on or off.
+ * @blink: Turn cursor blink on or off.
+ * @lines: One or two lines.
+ * @redefine_char: Redefine the actual pixel matrix of character.
+ */
+struct charlcd_ops {
+	void (*backlight)(struct charlcd *lcd, enum charlcd_onoff on);
+	int (*print)(struct charlcd *lcd, int c);
+	int (*gotoxy)(struct charlcd *lcd, unsigned int x, unsigned int y);
+	int (*home)(struct charlcd *lcd);
+	int (*clear_display)(struct charlcd *lcd);
+	int (*init_display)(struct charlcd *lcd);
+	int (*shift_cursor)(struct charlcd *lcd, enum charlcd_shift_dir dir);
+	int (*shift_display)(struct charlcd *lcd, enum charlcd_shift_dir dir);
+	int (*display)(struct charlcd *lcd, enum charlcd_onoff on);
+	int (*cursor)(struct charlcd *lcd, enum charlcd_onoff on);
+	int (*blink)(struct charlcd *lcd, enum charlcd_onoff on);
+	int (*fontsize)(struct charlcd *lcd, enum charlcd_fontsize size);
+	int (*lines)(struct charlcd *lcd, enum charlcd_lines lines);
+	int (*redefine_char)(struct charlcd *lcd, char *esc);
+};
+
+void charlcd_backlight(struct charlcd *lcd, enum charlcd_onoff on);
+
+struct charlcd *charlcd_alloc(unsigned int drvdata_size);
+void charlcd_free(struct charlcd *lcd);
+
+int charlcd_register(struct charlcd *lcd);
+int charlcd_unregister(struct charlcd *lcd);
+
+void charlcd_poke(struct charlcd *lcd);
+
+#endif /* CHARLCD_H */