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, 45 insertions, 0 deletions

diff --git a/Documentation/driver-api/tty/console.rst b/Documentation/driver-api/tty/console.rst
new file mode 100644
index 000000000..4348e36cd
--- /dev/null
+++ b/Documentation/driver-api/tty/console.rst
@@ -0,0 +1,45 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=======
+Console
+=======
+
+.. contents:: :local:
+
+Struct Console
+==============
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: console cons_flags
+
+Internals
+---------
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: nbcon_state nbcon_prio nbcon_context nbcon_write_context
+
+Struct Consw
+============
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: consw
+
+Console functions
+=================
+
+.. kernel-doc:: include/linux/console.h
+   :identifiers: console_srcu_read_flags console_srcu_write_flags
+        console_is_registered for_each_console_srcu for_each_console
+
+.. kernel-doc:: drivers/tty/vt/selection.c
+   :export:
+.. kernel-doc:: drivers/tty/vt/vt.c
+   :export:
+
+Internals
+---------
+
+.. kernel-doc:: drivers/tty/vt/selection.c
+   :internal:
+.. kernel-doc:: drivers/tty/vt/vt.c
+   :internal: