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, 315 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/penmount.c b/drivers/input/touchscreen/penmount.c
new file mode 100644
index 000000000..4b57b6664
--- /dev/null
+++ b/drivers/input/touchscreen/penmount.c
@@ -0,0 +1,315 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Penmount serial touchscreen driver
+ *
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ * Copyright (c) 2011 John Sung <penmount.touch@gmail.com>
+ *
+ * Based on ELO driver (drivers/input/touchscreen/elo.c)
+ * Copyright (c) 2004 Vojtech Pavlik
+ */
+
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/input/mt.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"PenMount serial touchscreen driver"
+
+MODULE_AUTHOR("Rick Koch <n1gp@hotmail.com>");
+MODULE_AUTHOR("John Sung <penmount.touch@gmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define	PM_MAX_LENGTH	6
+#define	PM_MAX_MTSLOT	16
+#define	PM_3000_MTSLOT	2
+#define	PM_6250_MTSLOT	12
+
+/*
+ * Multi-touch slot
+ */
+
+struct mt_slot {
+	unsigned short x, y;
+	bool active; /* is the touch valid? */
+};
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct pm {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[PM_MAX_LENGTH];
+	char phys[32];
+	unsigned char packetsize;
+	unsigned char maxcontacts;
+	struct mt_slot slots[PM_MAX_MTSLOT];
+	void (*parse_packet)(struct pm *);
+};
+
+/*
+ * pm_mtevent() sends mt events and also emulates pointer movement
+ */
+
+static void pm_mtevent(struct pm *pm, struct input_dev *input)
+{
+	int i;
+
+	for (i = 0; i < pm->maxcontacts; ++i) {
+		input_mt_slot(input, i);
+		input_mt_report_slot_state(input, MT_TOOL_FINGER,
+				pm->slots[i].active);
+		if (pm->slots[i].active) {
+			input_event(input, EV_ABS, ABS_MT_POSITION_X, pm->slots[i].x);
+			input_event(input, EV_ABS, ABS_MT_POSITION_Y, pm->slots[i].y);
+		}
+	}
+
+	input_mt_report_pointer_emulation(input, true);
+	input_sync(input);
+}
+
+/*
+ * pm_checkpacket() checks if data packet is valid
+ */
+
+static bool pm_checkpacket(unsigned char *packet)
+{
+	int total = 0;
+	int i;
+
+	for (i = 0; i < 5; i++)
+		total += packet[i];
+
+	return packet[5] == (unsigned char)~(total & 0xff);
+}
+
+static void pm_parse_9000(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0x80) && pm->packetsize == ++pm->idx) {
+		input_report_abs(dev, ABS_X, pm->data[1] * 128 + pm->data[2]);
+		input_report_abs(dev, ABS_Y, pm->data[3] * 128 + pm->data[4]);
+		input_report_key(dev, BTN_TOUCH, !!(pm->data[0] & 0x40));
+		input_sync(dev);
+		pm->idx = 0;
+	}
+}
+
+static void pm_parse_6000(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0xbf) == 0x30 && pm->packetsize == ++pm->idx) {
+		if (pm_checkpacket(pm->data)) {
+			input_report_abs(dev, ABS_X,
+					pm->data[2] * 256 + pm->data[1]);
+			input_report_abs(dev, ABS_Y,
+					pm->data[4] * 256 + pm->data[3]);
+			input_report_key(dev, BTN_TOUCH, pm->data[0] & 0x40);
+			input_sync(dev);
+		}
+		pm->idx = 0;
+	}
+}
+
+static void pm_parse_3000(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0xce) == 0x40 && pm->packetsize == ++pm->idx) {
+		if (pm_checkpacket(pm->data)) {
+			int slotnum = pm->data[0] & 0x0f;
+			pm->slots[slotnum].active = pm->data[0] & 0x30;
+			pm->slots[slotnum].x = pm->data[2] * 256 + pm->data[1];
+			pm->slots[slotnum].y = pm->data[4] * 256 + pm->data[3];
+			pm_mtevent(pm, dev);
+		}
+		pm->idx = 0;
+	}
+}
+
+static void pm_parse_6250(struct pm *pm)
+{
+	struct input_dev *dev = pm->dev;
+
+	if ((pm->data[0] & 0xb0) == 0x30 && pm->packetsize == ++pm->idx) {
+		if (pm_checkpacket(pm->data)) {
+			int slotnum = pm->data[0] & 0x0f;
+			pm->slots[slotnum].active = pm->data[0] & 0x40;
+			pm->slots[slotnum].x = pm->data[2] * 256 + pm->data[1];
+			pm->slots[slotnum].y = pm->data[4] * 256 + pm->data[3];
+			pm_mtevent(pm, dev);
+		}
+		pm->idx = 0;
+	}
+}
+
+static irqreturn_t pm_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct pm *pm = serio_get_drvdata(serio);
+
+	pm->data[pm->idx] = data;
+
+	pm->parse_packet(pm);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * pm_disconnect() is the opposite of pm_connect()
+ */
+
+static void pm_disconnect(struct serio *serio)
+{
+	struct pm *pm = serio_get_drvdata(serio);
+
+	serio_close(serio);
+
+	input_unregister_device(pm->dev);
+	kfree(pm);
+
+	serio_set_drvdata(serio, NULL);
+}
+
+/*
+ * pm_connect() is the routine that is called when someone adds a
+ * new serio device that supports PenMount protocol and registers it as
+ * an input device.
+ */
+
+static int pm_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct pm *pm;
+	struct input_dev *input_dev;
+	int max_x, max_y;
+	int err;
+
+	pm = kzalloc_obj(*pm);
+	input_dev = input_allocate_device();
+	if (!pm || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	pm->serio = serio;
+	pm->dev = input_dev;
+	scnprintf(pm->phys, sizeof(pm->phys), "%s/input0", serio->phys);
+	pm->maxcontacts = 1;
+
+	input_dev->name = "PenMount Serial TouchScreen";
+	input_dev->phys = pm->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_PENMOUNT;
+	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);
+
+	switch (serio->id.id) {
+	default:
+	case 0:
+		pm->packetsize = 5;
+		pm->parse_packet = pm_parse_9000;
+		input_dev->id.product = 0x9000;
+		max_x = max_y = 0x3ff;
+		break;
+
+	case 1:
+		pm->packetsize = 6;
+		pm->parse_packet = pm_parse_6000;
+		input_dev->id.product = 0x6000;
+		max_x = max_y = 0x3ff;
+		break;
+
+	case 2:
+		pm->packetsize = 6;
+		pm->parse_packet = pm_parse_3000;
+		input_dev->id.product = 0x3000;
+		max_x = max_y = 0x7ff;
+		pm->maxcontacts = PM_3000_MTSLOT;
+		break;
+
+	case 3:
+		pm->packetsize = 6;
+		pm->parse_packet = pm_parse_6250;
+		input_dev->id.product = 0x6250;
+		max_x = max_y = 0x3ff;
+		pm->maxcontacts = PM_6250_MTSLOT;
+		break;
+	}
+
+	input_set_abs_params(pm->dev, ABS_X, 0, max_x, 0, 0);
+	input_set_abs_params(pm->dev, ABS_Y, 0, max_y, 0, 0);
+
+	if (pm->maxcontacts > 1) {
+		input_mt_init_slots(pm->dev, pm->maxcontacts, 0);
+		input_set_abs_params(pm->dev,
+				     ABS_MT_POSITION_X, 0, max_x, 0, 0);
+		input_set_abs_params(pm->dev,
+				     ABS_MT_POSITION_Y, 0, max_y, 0, 0);
+	}
+
+	serio_set_drvdata(serio, pm);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(pm->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(pm);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id pm_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_PENMOUNT,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, pm_serio_ids);
+
+static struct serio_driver pm_drv = {
+	.driver		= {
+		.name	= "serio-penmount",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= pm_serio_ids,
+	.interrupt	= pm_interrupt,
+	.connect	= pm_connect,
+	.disconnect	= pm_disconnect,
+};
+
+module_serio_driver(pm_drv);