ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 184 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/touchwin.c b/drivers/input/touchscreen/touchwin.c
new file mode 100644
index 000000000..3ed33378d
--- /dev/null
+++ b/drivers/input/touchscreen/touchwin.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Touchwindow serial touchscreen driver
+ *
+ * Copyright (c) 2006 Rick Koch <n1gp@hotmail.com>
+ *
+ * Based on MicroTouch driver (drivers/input/touchscreen/mtouch.c)
+ * Copyright (c) 2004 Vojtech Pavlik
+ * and Dan Streetman <ddstreet@ieee.org>
+ */
+
+
+/*
+ * 2005/02/19 Rick Koch:
+ *   The Touchwindow I used is made by Edmark Corp. and
+ *   constantly outputs a stream of 0's unless it is touched.
+ *   It then outputs 3 bytes: X, Y, and a copy of Y.
+ */
+
+#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	"Touchwindow serial touchscreen driver"
+
+MODULE_AUTHOR("Rick Koch <n1gp@hotmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define TW_LENGTH 3
+
+#define TW_MIN_XC 0
+#define TW_MAX_XC 0xff
+#define TW_MIN_YC 0
+#define TW_MAX_YC 0xff
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct tw {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	int touched;
+	unsigned char data[TW_LENGTH];
+	char phys[32];
+};
+
+static irqreturn_t tw_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct tw *tw = serio_get_drvdata(serio);
+	struct input_dev *dev = tw->dev;
+
+	if (data) {		/* touch */
+		tw->touched = 1;
+		tw->data[tw->idx++] = data;
+		/* a full packet ends the accumulation, valid or not */
+		if (tw->idx == TW_LENGTH) {
+			/* report only if the two Y's are the same */
+			if (tw->data[1] == tw->data[2]) {
+				input_report_abs(dev, ABS_X, tw->data[0]);
+				input_report_abs(dev, ABS_Y, tw->data[1]);
+				input_report_key(dev, BTN_TOUCH, 1);
+				input_sync(dev);
+			}
+			tw->idx = 0;
+		}
+	} else if (tw->touched) {	/* untouch */
+		input_report_key(dev, BTN_TOUCH, 0);
+		input_sync(dev);
+		tw->idx = 0;
+		tw->touched = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * tw_disconnect() is the opposite of tw_connect()
+ */
+
+static void tw_disconnect(struct serio *serio)
+{
+	struct tw *tw = serio_get_drvdata(serio);
+
+	input_get_device(tw->dev);
+	input_unregister_device(tw->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(tw->dev);
+	kfree(tw);
+}
+
+/*
+ * tw_connect() is the routine that is called when someone adds a
+ * new serio device that supports the Touchwin protocol and registers it as
+ * an input device.
+ */
+
+static int tw_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct tw *tw;
+	struct input_dev *input_dev;
+	int err;
+
+	tw = kzalloc_obj(*tw);
+	input_dev = input_allocate_device();
+	if (!tw || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	tw->serio = serio;
+	tw->dev = input_dev;
+	scnprintf(tw->phys, sizeof(tw->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Touchwindow Serial TouchScreen";
+	input_dev->phys = tw->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TOUCHWIN;
+	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(tw->dev, ABS_X, TW_MIN_XC, TW_MAX_XC, 0, 0);
+	input_set_abs_params(tw->dev, ABS_Y, TW_MIN_YC, TW_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, tw);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(tw->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(tw);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id tw_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TOUCHWIN,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, tw_serio_ids);
+
+static struct serio_driver tw_drv = {
+	.driver		= {
+		.name	= "touchwin",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= tw_serio_ids,
+	.interrupt	= tw_interrupt,
+	.connect	= tw_connect,
+	.disconnect	= tw_disconnect,
+};
+
+module_serio_driver(tw_drv);