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, 86 insertions, 0 deletions

diff --git a/include/sound/seq_device.h b/include/sound/seq_device.h
new file mode 100644
index 000000000..3137d4c5f
--- /dev/null
+++ b/include/sound/seq_device.h
@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_SEQ_DEVICE_H
+#define __SOUND_SEQ_DEVICE_H
+
+/*
+ *  ALSA sequencer device management
+ *  Copyright (c) 1999 by Takashi Iwai <tiwai@suse.de>
+ */
+
+/*
+ * registered device information
+ */
+
+struct snd_seq_device {
+	/* device info */
+	struct snd_card *card;	/* sound card */
+	int device;		/* device number */
+	const char *id;		/* driver id */
+	char name[80];		/* device name */
+	int argsize;		/* size of the argument */
+	void *driver_data;	/* private data for driver */
+	void *private_data;	/* private data for the caller */
+	void (*private_free)(struct snd_seq_device *device);
+	struct device dev;
+	unsigned char args[];	/* driver-specific argument */
+};
+
+#define to_seq_dev(_dev) \
+	container_of(_dev, struct snd_seq_device, dev)
+
+/* sequencer driver */
+
+/* driver operators
+ * probe:
+ *	Initialize the device with given parameters.
+ *	Typically,
+ *		1. call snd_hwdep_new
+ *		2. allocate private data and initialize it
+ *		3. call snd_hwdep_register
+ *		4. store the instance to dev->driver_data pointer.
+ *		
+ * remove:
+ *	Release the private data.
+ *	Typically, call snd_device_free(dev->card, dev->driver_data)
+ */
+struct snd_seq_driver {
+	int (*probe)(struct snd_seq_device *dev);
+	void (*remove)(struct snd_seq_device *dev);
+	struct device_driver driver;
+	char *id;
+	int argsize;
+};
+
+#define to_seq_drv(_drv) \
+	container_of(_drv, struct snd_seq_driver, driver)
+
+/*
+ * prototypes
+ */
+#ifdef CONFIG_MODULES
+void snd_seq_device_load_drivers(void);
+#else
+#define snd_seq_device_load_drivers()
+#endif
+int snd_seq_device_new(struct snd_card *card, int device, const char *id,
+		       int argsize, struct snd_seq_device **result);
+
+#define SNDRV_SEQ_DEVICE_ARGPTR(dev) ((void *)(dev)->args)
+
+int __must_check __snd_seq_driver_register(struct snd_seq_driver *drv,
+					   struct module *mod);
+#define snd_seq_driver_register(drv) \
+	__snd_seq_driver_register(drv, THIS_MODULE)
+void snd_seq_driver_unregister(struct snd_seq_driver *drv);
+
+#define module_snd_seq_driver(drv) \
+	module_driver(drv, snd_seq_driver_register, snd_seq_driver_unregister)
+
+/*
+ * id strings for generic devices
+ */
+#define SNDRV_SEQ_DEV_ID_MIDISYNTH	"seq-midi"
+#define SNDRV_SEQ_DEV_ID_OPL3		"opl3-synth"
+#define SNDRV_SEQ_DEV_ID_UMP		"seq-ump-client"
+
+#endif /* __SOUND_SEQ_DEVICE_H */