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, 214 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/touchit213.c b/drivers/input/touchscreen/touchit213.c
new file mode 100644
index 000000000..6d4a1acf5
--- /dev/null
+++ b/drivers/input/touchscreen/touchit213.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Sahara TouchIT-213 serial touchscreen driver
+ *
+ * Copyright (c) 2007-2008 Claudio Nieder <private@claudio.ch>
+ *
+ * Based on Touchright driver (drivers/input/touchscreen/touchright.c)
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ * Copyright (c) 2004 Vojtech Pavlik
+ * and Dan Streetman <ddstreet@ieee.org>
+ */
+
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Sahara TouchIT-213 serial touchscreen driver"
+
+MODULE_AUTHOR("Claudio Nieder <private@claudio.ch>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+/*
+ * Data is received through COM1 at 9600bit/s,8bit,no parity in packets
+ * of 5 byte each.
+ *
+ *   +--------+   +--------+   +--------+   +--------+   +--------+
+ *   |1000000p|   |0xxxxxxx|   |0xxxxxxx|   |0yyyyyyy|   |0yyyyyyy|
+ *   +--------+   +--------+   +--------+   +--------+   +--------+
+ *                    MSB          LSB          MSB          LSB
+ *
+ * The value of p is 1 as long as the screen is touched and 0 when
+ * reporting the location where touching stopped, e.g. where the pen was
+ * lifted from the screen.
+ *
+ * When holding the screen in landscape mode as the BIOS text output is
+ * presented, x is the horizontal axis with values growing from left to
+ * right and y is the vertical axis with values growing from top to
+ * bottom.
+ *
+ * When holding the screen in portrait mode with the Sahara logo in its
+ * correct position, x ist the vertical axis with values growing from
+ * top to bottom and y is the horizontal axis with values growing from
+ * right to left.
+ */
+
+#define T213_FORMAT_TOUCH_BIT	0x01
+#define T213_FORMAT_STATUS_BYTE	0x80
+#define T213_FORMAT_STATUS_MASK	~T213_FORMAT_TOUCH_BIT
+
+/*
+ * On my Sahara Touch-IT 213 I have observed x values from 0 to 0x7f0
+ * and y values from 0x1d to 0x7e9, so the actual measurement is
+ * probably done with an 11 bit precision.
+ */
+#define T213_MIN_XC 0
+#define T213_MAX_XC 0x07ff
+#define T213_MIN_YC 0
+#define T213_MAX_YC 0x07ff
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct touchit213 {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char csum;
+	unsigned char data[5];
+	char phys[32];
+};
+
+static irqreturn_t touchit213_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct touchit213 *touchit213 = serio_get_drvdata(serio);
+	struct input_dev *dev = touchit213->dev;
+
+	touchit213->data[touchit213->idx] = data;
+
+	switch (touchit213->idx++) {
+	case 0:
+		if ((touchit213->data[0] & T213_FORMAT_STATUS_MASK) !=
+				T213_FORMAT_STATUS_BYTE) {
+			pr_debug("unsynchronized data: 0x%02x\n", data);
+			touchit213->idx = 0;
+		}
+		break;
+
+	case 4:
+		touchit213->idx = 0;
+		input_report_abs(dev, ABS_X,
+			(touchit213->data[1] << 7) | touchit213->data[2]);
+		input_report_abs(dev, ABS_Y,
+			(touchit213->data[3] << 7) | touchit213->data[4]);
+		input_report_key(dev, BTN_TOUCH,
+			touchit213->data[0] & T213_FORMAT_TOUCH_BIT);
+		input_sync(dev);
+		break;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * touchit213_disconnect() is the opposite of touchit213_connect()
+ */
+
+static void touchit213_disconnect(struct serio *serio)
+{
+	struct touchit213 *touchit213 = serio_get_drvdata(serio);
+
+	input_get_device(touchit213->dev);
+	input_unregister_device(touchit213->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(touchit213->dev);
+	kfree(touchit213);
+}
+
+/*
+ * touchit213_connect() is the routine that is called when someone adds a
+ * new serio device that supports the Touchright protocol and registers it as
+ * an input device.
+ */
+
+static int touchit213_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct touchit213 *touchit213;
+	struct input_dev *input_dev;
+	int err;
+
+	touchit213 = kzalloc_obj(*touchit213);
+	input_dev = input_allocate_device();
+	if (!touchit213 || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	touchit213->serio = serio;
+	touchit213->dev = input_dev;
+	scnprintf(touchit213->phys, sizeof(touchit213->phys),
+		  "%s/input0", serio->phys);
+
+	input_dev->name = "Sahara Touch-iT213 Serial TouchScreen";
+	input_dev->phys = touchit213->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TOUCHIT213;
+	input_dev->id.product = 0;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(touchit213->dev, ABS_X,
+			     T213_MIN_XC, T213_MAX_XC, 0, 0);
+	input_set_abs_params(touchit213->dev, ABS_Y,
+			     T213_MIN_YC, T213_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, touchit213);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(touchit213->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(touchit213);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id touchit213_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TOUCHIT213,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, touchit213_serio_ids);
+
+static struct serio_driver touchit213_drv = {
+	.driver		= {
+		.name	= "touchit213",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= touchit213_serio_ids,
+	.interrupt	= touchit213_interrupt,
+	.connect	= touchit213_connect,
+	.disconnect	= touchit213_disconnect,
+};
+
+module_serio_driver(touchit213_drv);