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

2 files changed, 381 insertions, 0 deletions

diff --git a/drivers/accessibility/braille/Makefile b/drivers/accessibility/braille/Makefile
new file mode 100644
index 000000000..fa4b87338
--- /dev/null
+++ b/drivers/accessibility/braille/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_A11Y_BRAILLE_CONSOLE)		+= braille_console.o
diff --git a/drivers/accessibility/braille/braille_console.c b/drivers/accessibility/braille/braille_console.c
new file mode 100644
index 000000000..06b43b678
--- /dev/null
+++ b/drivers/accessibility/braille/braille_console.c
@@ -0,0 +1,379 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Minimalistic braille device kernel support.
+ *
+ * By default, shows console messages on the braille device.
+ * Pressing Insert switches to VC browsing.
+ *
+ *  Copyright (C) Samuel Thibault <samuel.thibault@ens-lyon.org>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/console.h>
+#include <linux/notifier.h>
+
+#include <linux/selection.h>
+#include <linux/vt_kern.h>
+#include <linux/consolemap.h>
+
+#include <linux/keyboard.h>
+#include <linux/kbd_kern.h>
+#include <linux/input.h>
+
+MODULE_AUTHOR("samuel.thibault@ens-lyon.org");
+MODULE_DESCRIPTION("braille device");
+
+/*
+ * Braille device support part.
+ */
+
+/* Emit various sounds */
+static bool sound;
+module_param(sound, bool, 0);
+MODULE_PARM_DESC(sound, "emit sounds");
+
+static void beep(unsigned int freq)
+{
+	if (sound)
+		kd_mksound(freq, HZ/10);
+}
+
+/* mini console */
+#define WIDTH 40
+#define BRAILLE_KEY KEY_INSERT
+static u16 console_buf[WIDTH];
+static int console_cursor;
+
+/* mini view of VC */
+static int vc_x, vc_y, lastvc_x, lastvc_y;
+
+/* show console ? (or show VC) */
+static int console_show = 1;
+/* pending newline ? */
+static int console_newline = 1;
+static int lastVC = -1;
+
+static struct console *braille_co;
+
+/* Very VisioBraille-specific */
+static void braille_write(u16 *buf)
+{
+	static u16 lastwrite[WIDTH];
+	unsigned char data[1 + 1 + 2*WIDTH + 2 + 1], csum = 0, *c;
+	u16 out;
+	int i;
+
+	if (!braille_co)
+		return;
+
+	if (!memcmp(lastwrite, buf, WIDTH * sizeof(*buf)))
+		return;
+	memcpy(lastwrite, buf, WIDTH * sizeof(*buf));
+
+#define SOH 1
+#define STX 2
+#define ETX 2
+#define EOT 4
+#define ENQ 5
+	data[0] = STX;
+	data[1] = '>';
+	csum ^= '>';
+	c = &data[2];
+	for (i = 0; i < WIDTH; i++) {
+		out = buf[i];
+		if (out >= 0x100)
+			out = '?';
+		else if (out == 0x00)
+			out = ' ';
+		csum ^= out;
+		if (out <= 0x05) {
+			*c++ = SOH;
+			out |= 0x40;
+		}
+		*c++ = out;
+	}
+
+	if (csum <= 0x05) {
+		*c++ = SOH;
+		csum |= 0x40;
+	}
+	*c++ = csum;
+	*c++ = ETX;
+
+	braille_co->write(braille_co, data, c - data);
+}
+
+/* Follow the VC cursor*/
+static void vc_follow_cursor(struct vc_data *vc)
+{
+	vc_x = vc->state.x - (vc->state.x % WIDTH);
+	vc_y = vc->state.y;
+	lastvc_x = vc->state.x;
+	lastvc_y = vc->state.y;
+}
+
+/* Maybe the VC cursor moved, if so follow it */
+static void vc_maybe_cursor_moved(struct vc_data *vc)
+{
+	if (vc->state.x != lastvc_x || vc->state.y != lastvc_y)
+		vc_follow_cursor(vc);
+}
+
+/* Show portion of VC at vc_x, vc_y */
+static void vc_refresh(struct vc_data *vc)
+{
+	u16 buf[WIDTH];
+	int i;
+
+	for (i = 0; i < WIDTH; i++) {
+		u16 glyph = screen_glyph(vc,
+				2 * (vc_x + i) + vc_y * vc->vc_size_row);
+		buf[i] = inverse_translate(vc, glyph, true);
+	}
+	braille_write(buf);
+}
+
+/*
+ * Link to keyboard
+ */
+
+static int keyboard_notifier_call(struct notifier_block *blk,
+				  unsigned long code, void *_param)
+{
+	struct keyboard_notifier_param *param = _param;
+	struct vc_data *vc = param->vc;
+	int ret = NOTIFY_OK;
+
+	if (!param->down)
+		return ret;
+
+	switch (code) {
+	case KBD_KEYCODE:
+		if (console_show) {
+			if (param->value == BRAILLE_KEY) {
+				console_show = 0;
+				beep(880);
+				vc_maybe_cursor_moved(vc);
+				vc_refresh(vc);
+				ret = NOTIFY_STOP;
+			}
+		} else {
+			ret = NOTIFY_STOP;
+			switch (param->value) {
+			case KEY_INSERT:
+				beep(440);
+				console_show = 1;
+				lastVC = -1;
+				braille_write(console_buf);
+				break;
+			case KEY_LEFT:
+				if (vc_x > 0) {
+					vc_x -= WIDTH;
+					if (vc_x < 0)
+						vc_x = 0;
+				} else if (vc_y >= 1) {
+					beep(880);
+					vc_y--;
+					vc_x = vc->vc_cols-WIDTH;
+				} else
+					beep(220);
+				break;
+			case KEY_RIGHT:
+				if (vc_x + WIDTH < vc->vc_cols) {
+					vc_x += WIDTH;
+				} else if (vc_y + 1 < vc->vc_rows) {
+					beep(880);
+					vc_y++;
+					vc_x = 0;
+				} else
+					beep(220);
+				break;
+			case KEY_DOWN:
+				if (vc_y + 1 < vc->vc_rows)
+					vc_y++;
+				else
+					beep(220);
+				break;
+			case KEY_UP:
+				if (vc_y >= 1)
+					vc_y--;
+				else
+					beep(220);
+				break;
+			case KEY_HOME:
+				vc_follow_cursor(vc);
+				break;
+			case KEY_PAGEUP:
+				vc_x = 0;
+				vc_y = 0;
+				break;
+			case KEY_PAGEDOWN:
+				vc_x = 0;
+				vc_y = vc->vc_rows-1;
+				break;
+			default:
+				ret = NOTIFY_OK;
+				break;
+			}
+			if (ret == NOTIFY_STOP)
+				vc_refresh(vc);
+		}
+		break;
+	case KBD_POST_KEYSYM:
+	{
+		unsigned char type = KTYP(param->value) - 0xf0;
+
+		if (type == KT_SPEC) {
+			unsigned char val = KVAL(param->value);
+			int on_off = -1;
+
+			switch (val) {
+			case KVAL(K_CAPS):
+				on_off = vt_get_leds(fg_console, VC_CAPSLOCK);
+				break;
+			case KVAL(K_NUM):
+				on_off = vt_get_leds(fg_console, VC_NUMLOCK);
+				break;
+			case KVAL(K_HOLD):
+				on_off = vt_get_leds(fg_console, VC_SCROLLOCK);
+				break;
+			}
+			if (on_off == 1)
+				beep(880);
+			else if (on_off == 0)
+				beep(440);
+		}
+	}
+		break;
+	case KBD_UNBOUND_KEYCODE:
+	case KBD_UNICODE:
+	case KBD_KEYSYM:
+		/* Unused */
+		break;
+	}
+	return ret;
+}
+
+static struct notifier_block keyboard_notifier_block = {
+	.notifier_call = keyboard_notifier_call,
+};
+
+static int vt_notifier_call(struct notifier_block *blk,
+			    unsigned long code, void *_param)
+{
+	struct vt_notifier_param *param = _param;
+	struct vc_data *vc = param->vc;
+
+	switch (code) {
+	case VT_ALLOCATE:
+		break;
+	case VT_DEALLOCATE:
+		break;
+	case VT_WRITE:
+	{
+		unsigned char c = param->c;
+
+		if (vc->vc_num != fg_console)
+			break;
+		switch (c) {
+		case '\b':
+		case 127:
+			if (console_cursor > 0) {
+				console_cursor--;
+				console_buf[console_cursor] = ' ';
+			}
+			break;
+		case '\n':
+		case '\v':
+		case '\f':
+		case '\r':
+			console_newline = 1;
+			break;
+		case '\t':
+			c = ' ';
+			fallthrough;
+		default:
+			if (c < 32)
+				/* Ignore other control sequences */
+				break;
+			if (console_newline) {
+				memset(console_buf, 0, sizeof(console_buf));
+				console_cursor = 0;
+				console_newline = 0;
+			}
+			if (console_cursor == WIDTH)
+				memmove(console_buf, &console_buf[1],
+					(WIDTH-1) * sizeof(*console_buf));
+			else
+				console_cursor++;
+			console_buf[console_cursor-1] = c;
+			break;
+		}
+		if (console_show)
+			braille_write(console_buf);
+		else {
+			vc_maybe_cursor_moved(vc);
+			vc_refresh(vc);
+		}
+		break;
+	}
+	case VT_UPDATE:
+		/* Maybe a VT switch, flush */
+		if (console_show) {
+			if (vc->vc_num != lastVC) {
+				lastVC = vc->vc_num;
+				memset(console_buf, 0, sizeof(console_buf));
+				console_cursor = 0;
+				braille_write(console_buf);
+			}
+		} else {
+			vc_maybe_cursor_moved(vc);
+			vc_refresh(vc);
+		}
+		break;
+	}
+	return NOTIFY_OK;
+}
+
+static struct notifier_block vt_notifier_block = {
+	.notifier_call = vt_notifier_call,
+};
+
+/*
+ * Called from printk.c when console=brl is given
+ */
+
+int braille_register_console(struct console *console, int index,
+		char *console_options, char *braille_options)
+{
+	int ret;
+
+	if (!console_options)
+		/* Only support VisioBraille for now */
+		console_options = "57600o8";
+	if (braille_co)
+		return -ENODEV;
+	if (console->setup) {
+		ret = console->setup(console, console_options);
+		if (ret != 0)
+			return ret;
+	}
+	console->flags |= CON_ENABLED;
+	console->index = index;
+	braille_co = console;
+	register_keyboard_notifier(&keyboard_notifier_block);
+	register_vt_notifier(&vt_notifier_block);
+	return 1;
+}
+
+int braille_unregister_console(struct console *console)
+{
+	if (braille_co != console)
+		return -EINVAL;
+	unregister_keyboard_notifier(&keyboard_notifier_block);
+	unregister_vt_notifier(&vt_notifier_block);
+	braille_co = NULL;
+	return 1;
+}