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, 104 insertions, 0 deletions

diff --git a/drivers/scsi/arm/queue.h b/drivers/scsi/arm/queue.h
new file mode 100644
index 000000000..cb51379dc
--- /dev/null
+++ b/drivers/scsi/arm/queue.h
@@ -0,0 +1,104 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ *  linux/drivers/acorn/scsi/queue.h: queue handling
+ *
+ *  Copyright (C) 1997 Russell King
+ */
+#ifndef QUEUE_H
+#define QUEUE_H
+
+typedef struct {
+	struct list_head head;
+	struct list_head free;
+	spinlock_t queue_lock;
+	void *alloc;			/* start of allocated mem */
+} Queue_t;
+
+/*
+ * Function: void queue_initialise (Queue_t *queue)
+ * Purpose : initialise a queue
+ * Params  : queue - queue to initialise
+ */
+extern int queue_initialise (Queue_t *queue);
+
+/*
+ * Function: void queue_free (Queue_t *queue)
+ * Purpose : free a queue
+ * Params  : queue - queue to free
+ */
+extern void queue_free (Queue_t *queue);
+
+/*
+ * Function: struct scsi_cmnd *queue_remove (queue)
+ * Purpose : removes first SCSI command from a queue
+ * Params  : queue   - queue to remove command from
+ * Returns : struct scsi_cmnd if successful (and a reference), or NULL if no command available
+ */
+extern struct scsi_cmnd *queue_remove (Queue_t *queue);
+
+/*
+ * Function: struct scsi_cmnd *queue_remove_exclude_ref (queue, exclude)
+ * Purpose : remove a SCSI command from a queue
+ * Params  : queue   - queue to remove command from
+ *	     exclude - array of busy LUNs
+ * Returns : struct scsi_cmnd if successful (and a reference), or NULL if no command available
+ */
+extern struct scsi_cmnd *queue_remove_exclude(Queue_t *queue,
+					      unsigned long *exclude);
+
+#define queue_add_cmd_ordered(queue,SCpnt) \
+	__queue_add(queue,SCpnt,(SCpnt)->cmnd[0] == REQUEST_SENSE)
+#define queue_add_cmd_tail(queue,SCpnt) \
+	__queue_add(queue,SCpnt,0)
+/*
+ * Function: int __queue_add(Queue_t *queue, struct scsi_cmnd *SCpnt, int head)
+ * Purpose : Add a new command onto a queue
+ * Params  : queue - destination queue
+ *	     SCpnt - command to add
+ *	     head  - add command to head of queue
+ * Returns : 0 on error, !0 on success
+ */
+extern int __queue_add(Queue_t *queue, struct scsi_cmnd *SCpnt, int head);
+
+/*
+ * Function: struct scsi_cmnd *queue_remove_tgtluntag (queue, target, lun, tag)
+ * Purpose : remove a SCSI command from the queue for a specified target/lun/tag
+ * Params  : queue  - queue to remove command from
+ *	     target - target that we want
+ *	     lun    - lun on device
+ *	     tag    - tag on device
+ * Returns : struct scsi_cmnd if successful, or NULL if no command satisfies requirements
+ */
+extern struct scsi_cmnd *queue_remove_tgtluntag(Queue_t *queue, int target,
+						int lun, int tag);
+
+/*
+ * Function: queue_remove_all_target(queue, target)
+ * Purpose : remove all SCSI commands from the queue for a specified target
+ * Params  : queue  - queue to remove command from
+ *           target - target device id
+ * Returns : nothing
+ */
+extern void queue_remove_all_target(Queue_t *queue, int target);
+
+/*
+ * Function: int queue_probetgtlun (queue, target, lun)
+ * Purpose : check to see if we have a command in the queue for the specified
+ *	     target/lun.
+ * Params  : queue  - queue to look in
+ *	     target - target we want to probe
+ *	     lun    - lun on target
+ * Returns : 0 if not found, != 0 if found
+ */
+extern int queue_probetgtlun (Queue_t *queue, int target, int lun);
+
+/*
+ * Function: int queue_remove_cmd (Queue_t *queue, struct scsi_cmnd *SCpnt)
+ * Purpose : remove a specific command from the queues
+ * Params  : queue - queue to look in
+ *	     SCpnt - command to find
+ * Returns : 0 if not found
+ */
+int queue_remove_cmd(Queue_t *queue, struct scsi_cmnd *SCpnt);
+
+#endif /* QUEUE_H */