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, 19 insertions, 0 deletions

diff --git a/Documentation/sphinx/templates/kernel-toc.html b/Documentation/sphinx/templates/kernel-toc.html
new file mode 100644
index 000000000..b84969bd3
--- /dev/null
+++ b/Documentation/sphinx/templates/kernel-toc.html
@@ -0,0 +1,19 @@
+{# SPDX-License-Identifier: GPL-2.0 #}
+
+{# Create a local TOC the kernel way #}
+<p>
+<h3 class="kernel-toc-contents">Contents</h3>
+<input type="checkbox" class="kernel-toc-toggle" id = "kernel-toc-toggle" checked>
+<label class="kernel-toc-title" for="kernel-toc-toggle"></label>
+
+<div class="kerneltoc" id="kerneltoc">
+{{ toctree(maxdepth=3) }}
+</div>
+{# hacky script to try to position the left column #}
+<script type="text/javascript"> <!--
+  var sbar = document.getElementsByClassName("sphinxsidebar")[0];
+  let currents = document.getElementsByClassName("current")
+  if (currents.length) {
+    sbar.scrollTop = currents[currents.length - 1].offsetTop;
+  }
+  --> </script>