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, 21 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-ec b/Documentation/ABI/testing/debugfs-ec
new file mode 100644
index 000000000..ab6099daa
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-ec
@@ -0,0 +1,21 @@
+What:		/sys/kernel/debug/ec/*/{gpe,use_global_lock,io}
+Date:		July 2010
+Contact:	Thomas Renninger <trenn@suse.de>
+Description:
+
+General information like which GPE is assigned to the EC and whether
+the global lock should get used.
+Knowing the EC GPE one can watch the amount of HW events related to
+the EC here (XY -> GPE number from `/sys/kernel/debug/ec/*/gpe`):
+/sys/firmware/acpi/interrupts/gpeXY
+
+The io file is binary and a userspace tool located here:
+ftp://ftp.suse.com/pub/people/trenn/sources/ec/
+should get used to read out the 256 Embedded Controller registers
+or writing to them.
+
+CAUTION:
+  Do not write to the Embedded Controller if you don't know
+  what you are doing! Rebooting afterwards also is a good idea.
+  This can influence the way your machine is cooled and fans may
+  not get switched on again after you did a wrong write.