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, 26 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/vimc.dot b/Documentation/admin-guide/media/vimc.dot
new file mode 100644
index 000000000..92a5bb631
--- /dev/null
+++ b/Documentation/admin-guide/media/vimc.dot
@@ -0,0 +1,26 @@
+# SPDX-License-Identifier: GPL-2.0
+
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+	rankdir=TB
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+	n00000001:port0 -> n00000005:port0 [style=bold]
+	n00000001:port0 -> n0000000b [style=bold]
+	n00000001 -> n00000002
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+	n00000003 [label="{{} | Sensor B\n/dev/v4l-subdev1 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000003:port0 -> n00000008:port0 [style=bold]
+	n00000003:port0 -> n0000000f [style=bold]
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+	n00000005:port1 -> n00000015:port0
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+	n0000000f [label="Raw Capture 1\n/dev/video1", shape=box, style=filled, fillcolor=yellow]
+	n00000013 [label="{{} | RGB/YUV Input\n/dev/v4l-subdev4 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000013:port0 -> n00000015:port0 [style=dashed]
+	n00000015 [label="{{<port0> 0} | Scaler\n/dev/v4l-subdev5 | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
+	n00000015:port1 -> n00000018 [style=bold]
+	n00000018 [label="RGB/YUV Capture\n/dev/video2", shape=box, style=filled, fillcolor=yellow]
+}