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, 41 insertions, 0 deletions

diff --git a/Documentation/process/conclave.rst b/Documentation/process/conclave.rst
new file mode 100644
index 000000000..6a1234f54
--- /dev/null
+++ b/Documentation/process/conclave.rst
@@ -0,0 +1,41 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Linux kernel project continuity
+===============================
+
+The Linux kernel development project is widely distributed, with over
+100 maintainers each working to keep changes moving through their own
+repositories. The final step, though, is a centralized one where changes
+are pulled into the mainline repository. That is normally done by Linus
+Torvalds but, as was demonstrated by the 4.19 release in 2018, there are
+others who can do that work when the need arises.
+
+Should the maintainers of that repository become unwilling or unable to
+do that work going forward (including facilitating a transition), the
+project will need to find one or more replacements without delay. The
+process by which that will be done is listed below. $ORGANIZER is the
+last Maintainer Summit organizer or the current Linux Foundation (LF)
+Technical Advisory Board (TAB) Chair as a backup.
+
+- Within 72 hours, $ORGANIZER will open a discussion with the invitees
+  of the most recently concluded Maintainers Summit. A meeting of those
+  invitees and the TAB, either online or in-person, will be set as soon
+  as possible in a way that maximizes the number of people who can
+  participate.
+
+- If there has been no Maintainers Summit in the last 15 months, the set of
+  invitees for this meeting will be determined by the TAB.
+
+- The invitees to this meeting may bring in other maintainers as needed.
+
+- This meeting, chaired by $ORGANIZER, will consider options for the
+  ongoing management of the top-level kernel repository consistent with
+  the expectation that it maximizes the long term health of the project
+  and its community.
+
+- Within two weeks, a representative of this group will communicate to the
+  broader community, using the ksummit@lists.linux.dev mailing list, what
+  the next steps will be.
+
+The Linux Foundation, as guided by the TAB, will take the steps
+necessary to support and implement this plan.