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, 231 insertions, 0 deletions

diff --git a/drivers/input/joystick/fsia6b.c b/drivers/input/joystick/fsia6b.c
new file mode 100644
index 000000000..b0d736484
--- /dev/null
+++ b/drivers/input/joystick/fsia6b.c
@@ -0,0 +1,231 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * FS-iA6B iBus RC receiver driver
+ *
+ * This driver provides all 14 channels of the FlySky FS-ia6B RC receiver
+ * as analog values.
+ *
+ * Additionally, the channels can be converted to discrete switch values.
+ * By default, it is configured for the offical FS-i6 remote control.
+ * If you use a different hardware configuration, you can configure it
+ * using the `switch_config` parameter.
+ */
+
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/serio.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#define DRIVER_DESC		"FS-iA6B iBus RC receiver"
+
+MODULE_AUTHOR("Markus Koch <markus@notsyncing.net>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define IBUS_SERVO_COUNT	14
+
+static char *switch_config = "00000022320000";
+module_param(switch_config, charp, 0444);
+MODULE_PARM_DESC(switch_config,
+		 "Amount of switch positions per channel (14 characters, 0-3)");
+
+static int fsia6b_axes[IBUS_SERVO_COUNT] = {
+	ABS_X, ABS_Y,
+	ABS_Z, ABS_RX,
+	ABS_RY, ABS_RZ,
+	ABS_HAT0X, ABS_HAT0Y,
+	ABS_HAT1X, ABS_HAT1Y,
+	ABS_HAT2X, ABS_HAT2Y,
+	ABS_HAT3X, ABS_HAT3Y
+};
+
+enum ibus_state { SYNC, COLLECT, PROCESS };
+
+struct ibus_packet {
+	enum ibus_state state;
+
+	int offset;
+	u16 ibuf;
+	u16 channel[IBUS_SERVO_COUNT];
+};
+
+struct fsia6b {
+	struct input_dev *dev;
+	struct ibus_packet packet;
+
+	char phys[32];
+};
+
+static irqreturn_t fsia6b_serio_irq(struct serio *serio,
+				    unsigned char data, unsigned int flags)
+{
+	struct fsia6b *fsia6b = serio_get_drvdata(serio);
+	int i;
+	int sw_state;
+	int sw_id = BTN_0;
+
+	fsia6b->packet.ibuf = (data << 8) | ((fsia6b->packet.ibuf >> 8) & 0xFF);
+
+	switch (fsia6b->packet.state) {
+	case SYNC:
+		if (fsia6b->packet.ibuf == 0x4020)
+			fsia6b->packet.state = COLLECT;
+		break;
+
+	case COLLECT:
+		fsia6b->packet.state = PROCESS;
+		break;
+
+	case PROCESS:
+		fsia6b->packet.channel[fsia6b->packet.offset] =
+				fsia6b->packet.ibuf;
+		fsia6b->packet.offset++;
+
+		if (fsia6b->packet.offset == IBUS_SERVO_COUNT) {
+			fsia6b->packet.offset = 0;
+			fsia6b->packet.state = SYNC;
+			for (i = 0; i < IBUS_SERVO_COUNT; ++i) {
+				input_report_abs(fsia6b->dev, fsia6b_axes[i],
+						 fsia6b->packet.channel[i]);
+
+				sw_state = 0;
+				if (fsia6b->packet.channel[i] > 1900)
+					sw_state = 1;
+				else if (fsia6b->packet.channel[i] < 1100)
+					sw_state = 2;
+
+				switch (switch_config[i]) {
+				case '3':
+					input_report_key(fsia6b->dev,
+							 sw_id++,
+							 sw_state == 0);
+					fallthrough;
+				case '2':
+					input_report_key(fsia6b->dev,
+							 sw_id++,
+							 sw_state == 1);
+					fallthrough;
+				case '1':
+					input_report_key(fsia6b->dev,
+							 sw_id++,
+							 sw_state == 2);
+				}
+			}
+			input_sync(fsia6b->dev);
+		} else {
+			fsia6b->packet.state = COLLECT;
+		}
+		break;
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int fsia6b_serio_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct fsia6b *fsia6b;
+	struct input_dev *input_dev;
+	int err;
+	int i, j;
+	int sw_id = 0;
+
+	fsia6b = kzalloc_obj(*fsia6b);
+	if (!fsia6b)
+		return -ENOMEM;
+
+	fsia6b->packet.ibuf = 0;
+	fsia6b->packet.offset = 0;
+	fsia6b->packet.state = SYNC;
+
+	serio_set_drvdata(serio, fsia6b);
+
+	input_dev = input_allocate_device();
+	if (!input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+	fsia6b->dev = input_dev;
+
+	scnprintf(fsia6b->phys, sizeof(fsia6b->phys), "%s/input0", serio->phys);
+
+	input_dev->name = DRIVER_DESC;
+	input_dev->phys = fsia6b->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_FSIA6B;
+	input_dev->id.product = serio->id.id;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	for (i = 0; i < IBUS_SERVO_COUNT; i++)
+		input_set_abs_params(input_dev, fsia6b_axes[i],
+				     1000, 2000, 2, 2);
+
+	/* Register switch configuration */
+	for (i = 0; i < IBUS_SERVO_COUNT; i++) {
+		if (switch_config[i] < '0' || switch_config[i] > '3') {
+			dev_err(&fsia6b->dev->dev,
+				"Invalid switch configuration supplied for fsia6b.\n");
+			err = -EINVAL;
+			goto fail2;
+		}
+
+		for (j = '1'; j <= switch_config[i]; j++) {
+			input_set_capability(input_dev, EV_KEY, BTN_0 + sw_id);
+			sw_id++;
+		}
+	}
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(fsia6b->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+fail3:	serio_close(serio);
+fail2:	input_free_device(input_dev);
+fail1:	serio_set_drvdata(serio, NULL);
+	kfree(fsia6b);
+	return err;
+}
+
+static void fsia6b_serio_disconnect(struct serio *serio)
+{
+	struct fsia6b *fsia6b = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(fsia6b->dev);
+	kfree(fsia6b);
+}
+
+static const struct serio_device_id fsia6b_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_FSIA6B,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, fsia6b_serio_ids);
+
+static struct serio_driver fsia6b_serio_drv = {
+	.driver		= {
+		.name	= "fsia6b"
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= fsia6b_serio_ids,
+	.interrupt	= fsia6b_serio_irq,
+	.connect	= fsia6b_serio_connect,
+	.disconnect	= fsia6b_serio_disconnect
+};
+
+module_serio_driver(fsia6b_serio_drv)