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, 142 insertions, 0 deletions

diff --git a/drivers/input/joystick/joydump.c b/drivers/input/joystick/joydump.c
new file mode 100644
index 000000000..c9cbdcc7f
--- /dev/null
+++ b/drivers/input/joystick/joydump.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 1996-2001 Vojtech Pavlik
+ */
+
+/*
+ * This is just a very simple driver that can dump the data
+ * out of the joystick port into the syslog ...
+ */
+
+#include <linux/module.h>
+#include <linux/gameport.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+
+#define DRIVER_DESC	"Gameport data dumper module"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define BUF_SIZE 256
+
+struct joydump {
+	unsigned int time;
+	unsigned char data;
+};
+
+static int joydump_connect(struct gameport *gameport, struct gameport_driver *drv)
+{
+	struct joydump *buf;	/* all entries */
+	struct joydump *dump, *prev;	/* one entry each */
+	int axes[4], buttons;
+	int i, j, t, timeout;
+	unsigned long flags;
+	unsigned char u;
+
+	printk(KERN_INFO "joydump: ,------------------ START ----------------.\n");
+	printk(KERN_INFO "joydump: | Dumping: %30s |\n", gameport->phys);
+	printk(KERN_INFO "joydump: | Speed: %28d kHz |\n", gameport->speed);
+
+	if (gameport_open(gameport, drv, GAMEPORT_MODE_RAW)) {
+
+		printk(KERN_INFO "joydump: | Raw mode not available - trying cooked.    |\n");
+
+		if (gameport_open(gameport, drv, GAMEPORT_MODE_COOKED)) {
+
+			printk(KERN_INFO "joydump: | Cooked not available either. Failing.   |\n");
+			printk(KERN_INFO "joydump: `------------------- END -----------------'\n");
+			return -ENODEV;
+		}
+
+		gameport_cooked_read(gameport, axes, &buttons);
+
+		for (i = 0; i < 4; i++)
+			printk(KERN_INFO "joydump: | Axis %d: %4d.                           |\n", i, axes[i]);
+		printk(KERN_INFO "joydump: | Buttons %02x.                             |\n", buttons);
+		printk(KERN_INFO "joydump: `------------------- END -----------------'\n");
+	}
+
+	timeout = gameport_time(gameport, 10000); /* 10 ms */
+
+	buf = kmalloc_objs(struct joydump, BUF_SIZE);
+	if (!buf) {
+		printk(KERN_INFO "joydump: no memory for testing\n");
+		goto jd_end;
+	}
+	dump = buf;
+	t = 0;
+	i = 1;
+
+	local_irq_save(flags);
+
+	u = gameport_read(gameport);
+
+	dump->data = u;
+	dump->time = t;
+	dump++;
+
+	gameport_trigger(gameport);
+
+	while (i < BUF_SIZE && t < timeout) {
+
+		dump->data = gameport_read(gameport);
+
+		if (dump->data ^ u) {
+			u = dump->data;
+			dump->time = t;
+			i++;
+			dump++;
+		}
+		t++;
+	}
+
+	local_irq_restore(flags);
+
+/*
+ * Dump data.
+ */
+
+	t = i;
+	dump = buf;
+	prev = dump;
+
+	printk(KERN_INFO "joydump: >------------------ DATA -----------------<\n");
+	printk(KERN_INFO "joydump: | index: %3d delta: %3d us data: ", 0, 0);
+	for (j = 7; j >= 0; j--)
+		printk("%d", (dump->data >> j) & 1);
+	printk(" |\n");
+	dump++;
+
+	for (i = 1; i < t; i++, dump++, prev++) {
+		printk(KERN_INFO "joydump: | index: %3d delta: %3d us data: ",
+			i, dump->time - prev->time);
+		for (j = 7; j >= 0; j--)
+			printk("%d", (dump->data >> j) & 1);
+		printk(" |\n");
+	}
+	kfree(buf);
+
+jd_end:
+	printk(KERN_INFO "joydump: `------------------- END -----------------'\n");
+
+	return 0;
+}
+
+static void joydump_disconnect(struct gameport *gameport)
+{
+	gameport_close(gameport);
+}
+
+static struct gameport_driver joydump_drv = {
+	.driver		= {
+		.name	= "joydump",
+	},
+	.description	= DRIVER_DESC,
+	.connect	= joydump_connect,
+	.disconnect	= joydump_disconnect,
+};
+
+module_gameport_driver(joydump_drv);