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, 102 insertions, 0 deletions

diff --git a/include/sound/seq_kernel.h b/include/sound/seq_kernel.h
new file mode 100644
index 000000000..00c32eed2
--- /dev/null
+++ b/include/sound/seq_kernel.h
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_SEQ_KERNEL_H
+#define __SOUND_SEQ_KERNEL_H
+
+/*
+ *  Main kernel header file for the ALSA sequencer
+ *  Copyright (c) 1998 by Frank van de Pol <fvdpol@coil.demon.nl>
+ */
+#include <linux/time.h>
+#include <sound/asequencer.h>
+
+typedef struct snd_seq_real_time snd_seq_real_time_t;
+typedef union snd_seq_timestamp snd_seq_timestamp_t;
+
+/* maximum number of queues */
+#define SNDRV_SEQ_MAX_QUEUES		32
+
+/* max number of concurrent clients */
+#define SNDRV_SEQ_MAX_CLIENTS 		192
+
+/* max number of concurrent ports */
+#define SNDRV_SEQ_MAX_PORTS 		254
+
+/* max number of events in memory pool */
+#define SNDRV_SEQ_MAX_EVENTS		2000
+
+/* default number of events in memory pool */
+#define SNDRV_SEQ_DEFAULT_EVENTS	500
+
+/* max number of events in memory pool for one client (outqueue) */
+#define SNDRV_SEQ_MAX_CLIENT_EVENTS	2000
+
+/* default number of events in memory pool for one client (outqueue) */
+#define SNDRV_SEQ_DEFAULT_CLIENT_EVENTS	200
+
+/* max delivery path length */
+/* NOTE: this shouldn't be greater than MAX_LOCKDEP_SUBCLASSES */
+#define SNDRV_SEQ_MAX_HOPS		8
+
+/* max size of event size */
+#define SNDRV_SEQ_MAX_EVENT_LEN		0x3fffffff
+
+/* call-backs for kernel port */
+struct snd_seq_port_callback {
+	struct module *owner;
+	void *private_data;
+	int (*subscribe)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*unsubscribe)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*use)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*unuse)(void *private_data, struct snd_seq_port_subscribe *info);
+	int (*event_input)(struct snd_seq_event *ev, int direct, void *private_data, int atomic, int hop);
+	void (*private_free)(void *private_data);
+	/*...*/
+};
+
+/* interface for kernel client */
+__printf(3, 4)
+int snd_seq_create_kernel_client(struct snd_card *card, int client_index,
+				 const char *name_fmt, ...);
+int snd_seq_delete_kernel_client(int client);
+int snd_seq_kernel_client_enqueue(int client, struct snd_seq_event *ev,
+				  struct file *file, bool blocking);
+int snd_seq_kernel_client_dispatch(int client, struct snd_seq_event *ev, int atomic, int hop);
+int snd_seq_kernel_client_ctl(int client, unsigned int cmd, void *arg);
+
+#define SNDRV_SEQ_EXT_MASK	0xc0000000
+#define SNDRV_SEQ_EXT_USRPTR	0x80000000
+#define SNDRV_SEQ_EXT_CHAINED	0x40000000
+
+typedef int (*snd_seq_dump_func_t)(void *ptr, void *buf, int count);
+int snd_seq_expand_var_event(const struct snd_seq_event *event, int count, char *buf,
+			     int in_kernel, int size_aligned);
+int snd_seq_expand_var_event_at(const struct snd_seq_event *event, int count,
+				char *buf, int offset);
+int snd_seq_dump_var_event(const struct snd_seq_event *event,
+			   snd_seq_dump_func_t func, void *private_data);
+
+/* size of the event packet; it can be greater than snd_seq_event size */
+static inline size_t snd_seq_event_packet_size(struct snd_seq_event *ev)
+{
+	if (snd_seq_ev_is_ump(ev))
+		return sizeof(struct snd_seq_ump_event);
+	return sizeof(struct snd_seq_event);
+}
+
+/* interface for OSS emulation */
+int snd_seq_set_queue_tempo(int client, struct snd_seq_queue_tempo *tempo);
+
+/* port attach/detach */
+int snd_seq_event_port_attach(int client, struct snd_seq_port_callback *pcbp,
+			      int cap, int type, int midi_channels, int midi_voices, char *portname);
+int snd_seq_event_port_detach(int client, int port);
+
+#ifdef CONFIG_MODULES
+void snd_seq_autoload_init(void);
+void snd_seq_autoload_exit(void);
+#else
+#define snd_seq_autoload_init()
+#define snd_seq_autoload_exit()
+#endif
+
+#endif /* __SOUND_SEQ_KERNEL_H */