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, 174 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/touchright.c b/drivers/input/touchscreen/touchright.c
new file mode 100644
index 000000000..d7fdf201e
--- /dev/null
+++ b/drivers/input/touchscreen/touchright.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Touchright 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>
+ */
+
+
+#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	"Touchright serial touchscreen driver"
+
+MODULE_AUTHOR("Rick Koch <n1gp@hotmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define TR_FORMAT_TOUCH_BIT	0x01
+#define TR_FORMAT_STATUS_BYTE	0x40
+#define TR_FORMAT_STATUS_MASK	~TR_FORMAT_TOUCH_BIT
+
+#define TR_LENGTH 5
+
+#define TR_MIN_XC 0
+#define TR_MAX_XC 0x1ff
+#define TR_MIN_YC 0
+#define TR_MAX_YC 0x1ff
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct tr {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[TR_LENGTH];
+	char phys[32];
+};
+
+static irqreturn_t tr_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct tr *tr = serio_get_drvdata(serio);
+	struct input_dev *dev = tr->dev;
+
+	tr->data[tr->idx] = data;
+
+	if ((tr->data[0] & TR_FORMAT_STATUS_MASK) == TR_FORMAT_STATUS_BYTE) {
+		if (++tr->idx == TR_LENGTH) {
+			input_report_abs(dev, ABS_X,
+				(tr->data[1] << 5) | (tr->data[2] >> 1));
+			input_report_abs(dev, ABS_Y,
+				(tr->data[3] << 5) | (tr->data[4] >> 1));
+			input_report_key(dev, BTN_TOUCH,
+				tr->data[0] & TR_FORMAT_TOUCH_BIT);
+			input_sync(dev);
+			tr->idx = 0;
+		}
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * tr_disconnect() is the opposite of tr_connect()
+ */
+
+static void tr_disconnect(struct serio *serio)
+{
+	struct tr *tr = serio_get_drvdata(serio);
+
+	input_get_device(tr->dev);
+	input_unregister_device(tr->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(tr->dev);
+	kfree(tr);
+}
+
+/*
+ * tr_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 tr_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct tr *tr;
+	struct input_dev *input_dev;
+	int err;
+
+	tr = kzalloc_obj(*tr);
+	input_dev = input_allocate_device();
+	if (!tr || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	tr->serio = serio;
+	tr->dev = input_dev;
+	scnprintf(tr->phys, sizeof(tr->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Touchright Serial TouchScreen";
+	input_dev->phys = tr->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TOUCHRIGHT;
+	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(tr->dev, ABS_X, TR_MIN_XC, TR_MAX_XC, 0, 0);
+	input_set_abs_params(tr->dev, ABS_Y, TR_MIN_YC, TR_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, tr);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(tr->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(tr);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id tr_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TOUCHRIGHT,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, tr_serio_ids);
+
+static struct serio_driver tr_drv = {
+	.driver		= {
+		.name	= "touchright",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= tr_serio_ids,
+	.interrupt	= tr_interrupt,
+	.connect	= tr_connect,
+	.disconnect	= tr_disconnect,
+};
+
+module_serio_driver(tr_drv);