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, 244 insertions, 0 deletions

diff --git a/drivers/input/joystick/twidjoy.c b/drivers/input/joystick/twidjoy.c
new file mode 100644
index 000000000..fb452552c
--- /dev/null
+++ b/drivers/input/joystick/twidjoy.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2001 Arndt Schoenewald
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *  Copyright (c) 2000 Mark Fletcher
+ *
+ *  Sponsored by Quelltext AG (http://www.quelltext-ag.de), Dortmund, Germany
+ */
+
+/*
+ * Driver to use Handykey's Twiddler (the first edition, i.e. the one with
+ * the RS232 interface) as a joystick under Linux
+ *
+ * The Twiddler is a one-handed chording keyboard featuring twelve buttons on
+ * the front, six buttons on the top, and a built-in tilt sensor. The buttons
+ * on the front, which are grouped as four rows of three buttons, are pressed
+ * by the four fingers (this implies only one button per row can be held down
+ * at the same time) and the buttons on the top are for the thumb. The tilt
+ * sensor delivers X and Y axis data depending on how the Twiddler is held.
+ * Additional information can be found at http://www.handykey.com.
+ *
+ * This driver does not use the Twiddler for its intended purpose, i.e. as
+ * a chording keyboard, but as a joystick: pressing and releasing a button
+ * immediately sends a corresponding button event, and tilting it generates
+ * corresponding ABS_X and ABS_Y events. This turns the Twiddler into a game
+ * controller with amazing 18 buttons :-)
+ *
+ * Note: The Twiddler2 (the successor of the Twiddler that connects directly
+ * to the PS/2 keyboard and mouse ports) is NOT supported by this driver!
+ *
+ * For questions or feedback regarding this driver module please contact:
+ * Arndt Schoenewald <arndt@quelltext.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Handykey Twiddler keyboard as a joystick driver"
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Constants.
+ */
+
+#define TWIDJOY_MAX_LENGTH 5
+
+static struct twidjoy_button_spec {
+	int bitshift;
+	int bitmask;
+	int buttons[3];
+}
+twidjoy_buttons[] = {
+	{  0, 3, { BTN_A,      BTN_B,     BTN_C    } },
+	{  2, 3, { BTN_X,      BTN_Y,     BTN_Z    } },
+	{  4, 3, { BTN_TL,     BTN_TR,    BTN_TR2  } },
+	{  6, 3, { BTN_SELECT, BTN_START, BTN_MODE } },
+	{  8, 1, { BTN_BASE5                       } },
+	{  9, 1, { BTN_BASE                        } },
+	{ 10, 1, { BTN_BASE3                       } },
+	{ 11, 1, { BTN_BASE4                       } },
+	{ 12, 1, { BTN_BASE2                       } },
+	{ 13, 1, { BTN_BASE6                       } },
+	{ 0,  0, { 0                               } }
+};
+
+/*
+ * Per-Twiddler data.
+ */
+
+struct twidjoy {
+	struct input_dev *dev;
+	int idx;
+	unsigned char data[TWIDJOY_MAX_LENGTH];
+	char phys[32];
+};
+
+/*
+ * twidjoy_process_packet() decodes packets the driver receives from the
+ * Twiddler. It updates the data accordingly.
+ */
+
+static void twidjoy_process_packet(struct twidjoy *twidjoy)
+{
+	struct input_dev *dev = twidjoy->dev;
+	unsigned char *data = twidjoy->data;
+	struct twidjoy_button_spec *bp;
+	int button_bits, abs_x, abs_y;
+
+	button_bits = ((data[1] & 0x7f) << 7) | (data[0] & 0x7f);
+
+	for (bp = twidjoy_buttons; bp->bitmask; bp++) {
+		int value = (button_bits & (bp->bitmask << bp->bitshift)) >> bp->bitshift;
+		int i;
+
+		for (i = 0; i < bp->bitmask; i++)
+			input_report_key(dev, bp->buttons[i], i+1 == value);
+	}
+
+	abs_x = ((data[4] & 0x07) << 5) | ((data[3] & 0x7C) >> 2);
+	if (data[4] & 0x08) abs_x -= 256;
+
+	abs_y = ((data[3] & 0x01) << 7) | ((data[2] & 0x7F) >> 0);
+	if (data[3] & 0x02) abs_y -= 256;
+
+	input_report_abs(dev, ABS_X, -abs_x);
+	input_report_abs(dev, ABS_Y, +abs_y);
+
+	input_sync(dev);
+}
+
+/*
+ * twidjoy_interrupt() is called by the low level driver when characters
+ * are ready for us. We then buffer them for further processing, or call the
+ * packet processing routine.
+ */
+
+static irqreturn_t twidjoy_interrupt(struct serio *serio, unsigned char data, unsigned int flags)
+{
+	struct twidjoy *twidjoy = serio_get_drvdata(serio);
+
+	/* All Twiddler packets are 5 bytes. The fact that the first byte
+	 * has a MSB of 0 and all other bytes have a MSB of 1 can be used
+	 * to check and regain sync. */
+
+	if ((data & 0x80) == 0)
+		twidjoy->idx = 0;	/* this byte starts a new packet */
+	else if (twidjoy->idx == 0)
+		return IRQ_HANDLED;	/* wrong MSB -- ignore this byte */
+
+	if (twidjoy->idx < TWIDJOY_MAX_LENGTH)
+		twidjoy->data[twidjoy->idx++] = data;
+
+	if (twidjoy->idx == TWIDJOY_MAX_LENGTH) {
+		twidjoy_process_packet(twidjoy);
+		twidjoy->idx = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * twidjoy_disconnect() is the opposite of twidjoy_connect()
+ */
+
+static void twidjoy_disconnect(struct serio *serio)
+{
+	struct twidjoy *twidjoy = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(twidjoy->dev);
+	kfree(twidjoy);
+}
+
+/*
+ * twidjoy_connect() is the routine that is called when someone adds a
+ * new serio device. It looks for the Twiddler, and if found, registers
+ * it as an input device.
+ */
+
+static int twidjoy_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct twidjoy_button_spec *bp;
+	struct twidjoy *twidjoy;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+	int i;
+
+	twidjoy = kzalloc_obj(*twidjoy);
+	input_dev = input_allocate_device();
+	if (!twidjoy || !input_dev)
+		goto fail1;
+
+	twidjoy->dev = input_dev;
+	snprintf(twidjoy->phys, sizeof(twidjoy->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Handykey Twiddler";
+	input_dev->phys = twidjoy->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TWIDJOY;
+	input_dev->id.product = 0x0001;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_set_abs_params(input_dev, ABS_X, -50, 50, 4, 4);
+	input_set_abs_params(input_dev, ABS_Y, -50, 50, 4, 4);
+
+	for (bp = twidjoy_buttons; bp->bitmask; bp++)
+		for (i = 0; i < bp->bitmask; i++)
+			set_bit(bp->buttons[i], input_dev->keybit);
+
+	serio_set_drvdata(serio, twidjoy);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(twidjoy->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(twidjoy);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id twidjoy_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TWIDJOY,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, twidjoy_serio_ids);
+
+static struct serio_driver twidjoy_drv = {
+	.driver		= {
+		.name	= "twidjoy",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= twidjoy_serio_ids,
+	.interrupt	= twidjoy_interrupt,
+	.connect	= twidjoy_connect,
+	.disconnect	= twidjoy_disconnect,
+};
+
+module_serio_driver(twidjoy_drv);