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, 202 insertions, 0 deletions

diff --git a/drivers/input/joystick/zhenhua.c b/drivers/input/joystick/zhenhua.c
new file mode 100644
index 000000000..8ca189663
--- /dev/null
+++ b/drivers/input/joystick/zhenhua.c
@@ -0,0 +1,202 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  derived from "twidjoy.c"
+ *
+ *  Copyright (c) 2008 Martin Kebert
+ *  Copyright (c) 2001 Arndt Schoenewald
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *  Copyright (c) 2000 Mark Fletcher
+ */
+
+/*
+ * Driver to use 4CH RC transmitter using Zhen Hua 5-byte protocol (Walkera Lama,
+ * EasyCopter etc.) as a joystick under Linux.
+ *
+ * RC transmitters using Zhen Hua 5-byte protocol are cheap four channels
+ * transmitters for control a RC planes or RC helicopters with possibility to
+ * connect on a serial port.
+ * Data coming from transmitter is in this order:
+ * 1. byte = synchronisation byte
+ * 2. byte = X axis
+ * 3. byte = Y axis
+ * 4. byte = RZ axis
+ * 5. byte = Z axis
+ * (and this is repeated)
+ *
+ * For questions or feedback regarding this driver module please contact:
+ * Martin Kebert <gkmarty@gmail.com> - but I am not a C-programmer nor kernel
+ * coder :-(
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/bitrev.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"RC transmitter with 5-byte Zhen Hua protocol joystick driver"
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Constants.
+ */
+
+#define ZHENHUA_MAX_LENGTH 5
+
+/*
+ * Zhen Hua data.
+ */
+
+struct zhenhua {
+	struct input_dev *dev;
+	int idx;
+	unsigned char data[ZHENHUA_MAX_LENGTH];
+	char phys[32];
+};
+
+/*
+ * zhenhua_process_packet() decodes packets the driver receives from the
+ * RC transmitter. It updates the data accordingly.
+ */
+
+static void zhenhua_process_packet(struct zhenhua *zhenhua)
+{
+	struct input_dev *dev = zhenhua->dev;
+	unsigned char *data = zhenhua->data;
+
+	input_report_abs(dev, ABS_Y, data[1]);
+	input_report_abs(dev, ABS_X, data[2]);
+	input_report_abs(dev, ABS_RZ, data[3]);
+	input_report_abs(dev, ABS_Z, data[4]);
+
+	input_sync(dev);
+}
+
+/*
+ * zhenhua_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 zhenhua_interrupt(struct serio *serio, unsigned char data, unsigned int flags)
+{
+	struct zhenhua *zhenhua = serio_get_drvdata(serio);
+
+	/* All Zhen Hua packets are 5 bytes. The fact that the first byte
+	 * is allways 0xf7 and all others are in range 0x32 - 0xc8 (50-200)
+	 * can be used to check and regain sync. */
+
+	if (data == 0xef)
+		zhenhua->idx = 0;	/* this byte starts a new packet */
+	else if (zhenhua->idx == 0)
+		return IRQ_HANDLED;	/* wrong MSB -- ignore this byte */
+
+	if (zhenhua->idx < ZHENHUA_MAX_LENGTH)
+		zhenhua->data[zhenhua->idx++] = bitrev8(data);
+
+	if (zhenhua->idx == ZHENHUA_MAX_LENGTH) {
+		zhenhua_process_packet(zhenhua);
+		zhenhua->idx = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * zhenhua_disconnect() is the opposite of zhenhua_connect()
+ */
+
+static void zhenhua_disconnect(struct serio *serio)
+{
+	struct zhenhua *zhenhua = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(zhenhua->dev);
+	kfree(zhenhua);
+}
+
+/*
+ * zhenhua_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 zhenhua_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct zhenhua *zhenhua;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+
+	zhenhua = kzalloc_obj(*zhenhua);
+	input_dev = input_allocate_device();
+	if (!zhenhua || !input_dev)
+		goto fail1;
+
+	zhenhua->dev = input_dev;
+	snprintf(zhenhua->phys, sizeof(zhenhua->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Zhen Hua 5-byte device";
+	input_dev->phys = zhenhua->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_ZHENHUA;
+	input_dev->id.product = 0x0001;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	input_dev->evbit[0] = BIT(EV_ABS);
+	input_set_abs_params(input_dev, ABS_X, 50, 200, 0, 0);
+	input_set_abs_params(input_dev, ABS_Y, 50, 200, 0, 0);
+	input_set_abs_params(input_dev, ABS_Z, 50, 200, 0, 0);
+	input_set_abs_params(input_dev, ABS_RZ, 50, 200, 0, 0);
+
+	serio_set_drvdata(serio, zhenhua);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(zhenhua->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(zhenhua);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id zhenhua_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_ZHENHUA,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, zhenhua_serio_ids);
+
+static struct serio_driver zhenhua_drv = {
+	.driver		= {
+		.name	= "zhenhua",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= zhenhua_serio_ids,
+	.interrupt	= zhenhua_interrupt,
+	.connect	= zhenhua_connect,
+	.disconnect	= zhenhua_disconnect,
+};
+
+module_serio_driver(zhenhua_drv);