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, 83 insertions, 0 deletions

diff --git a/include/sound/seq_oss.h b/include/sound/seq_oss.h
new file mode 100644
index 000000000..7bf10a0fa
--- /dev/null
+++ b/include/sound/seq_oss.h
@@ -0,0 +1,83 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_SEQ_OSS_H
+#define __SOUND_SEQ_OSS_H
+
+/*
+ * OSS compatible sequencer driver
+ *
+ * Copyright (C) 1998,99 Takashi Iwai
+ */
+
+#include <sound/asequencer.h>
+#include <sound/seq_kernel.h>
+
+/*
+ * argument structure for synthesizer operations
+ */
+struct snd_seq_oss_arg {
+	/* given by OSS sequencer */
+	int app_index;	/* application unique index */
+	int file_mode;	/* file mode - see below */
+	int seq_mode;	/* sequencer mode - see below */
+
+	/* following must be initialized in open callback */
+	struct snd_seq_addr addr;	/* opened port address */
+	void *private_data;	/* private data for lowlevel drivers */
+
+	/* note-on event passing mode: initially given by OSS seq,
+	 * but configurable by drivers - see below
+	 */
+	int event_passing;
+};
+
+
+/*
+ * synthesizer operation callbacks
+ */
+struct snd_seq_oss_callback {
+	struct module *owner;
+	int (*open)(struct snd_seq_oss_arg *p, void *closure);
+	int (*close)(struct snd_seq_oss_arg *p);
+	int (*ioctl)(struct snd_seq_oss_arg *p, unsigned int cmd, unsigned long arg);
+	int (*load_patch)(struct snd_seq_oss_arg *p, int format, const char __user *buf, int offs, int count);
+	int (*reset)(struct snd_seq_oss_arg *p);
+	int (*raw_event)(struct snd_seq_oss_arg *p, unsigned char *data);
+};
+
+/* flag: file_mode */
+#define SNDRV_SEQ_OSS_FILE_ACMODE		3
+#define SNDRV_SEQ_OSS_FILE_READ		1
+#define SNDRV_SEQ_OSS_FILE_WRITE		2
+#define SNDRV_SEQ_OSS_FILE_NONBLOCK	4
+
+/* flag: seq_mode */
+#define SNDRV_SEQ_OSS_MODE_SYNTH		0
+#define SNDRV_SEQ_OSS_MODE_MUSIC		1
+
+/* flag: event_passing */
+#define SNDRV_SEQ_OSS_PROCESS_EVENTS	0	/* key == 255 is processed as velocity change */
+#define SNDRV_SEQ_OSS_PASS_EVENTS		1	/* pass all events to callback */
+#define SNDRV_SEQ_OSS_PROCESS_KEYPRESS	2	/* key >= 128 will be processed as key-pressure */
+
+/* default control rate: fixed */
+#define SNDRV_SEQ_OSS_CTRLRATE		100
+
+/* default max queue length: configurable by module option */
+#define SNDRV_SEQ_OSS_MAX_QLEN		1024
+
+
+/*
+ * data pointer to snd_seq_register_device
+ */
+struct snd_seq_oss_reg {
+	int type;
+	int subtype;
+	int nvoices;
+	struct snd_seq_oss_callback oper;
+	void *private_data;
+};
+
+/* device id */
+#define SNDRV_SEQ_DEV_ID_OSS		"seq-oss"
+
+#endif /* __SOUND_SEQ_OSS_H */