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, 84 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module
new file mode 100644
index 000000000..d5b7d19bd
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-module
@@ -0,0 +1,84 @@
+What:		/sys/module/pch_phub/drivers/.../pch_mac
+Date:		August 2010
+KernelVersion:	2.6.35
+Contact:	masa-korg@dsn.okisemi.com
+Description:	Write/read GbE MAC address.
+
+What:		/sys/module/pch_phub/drivers/.../pch_firmware
+Date:		August 2010
+KernelVersion:	2.6.35
+Contact:	masa-korg@dsn.okisemi.com
+Description:	Write/read Option ROM data.
+
+
+What:		/sys/module/ehci_hcd/drivers/.../uframe_periodic_max
+Date:		July 2011
+KernelVersion:	3.1
+Contact:	Kirill Smelkov <kirr@mns.spb.ru>
+Description:	Maximum time allowed for periodic transfers per microframe (μs)
+
+		Note:
+		  USB 2.0 sets maximum allowed time for periodic transfers per
+		  microframe to be 80%, that is 100 microseconds out of 125
+		  microseconds (full microframe).
+
+		  However there are cases, when 80% max isochronous bandwidth is
+		  too limiting. For example two video streams could require 110
+		  microseconds of isochronous bandwidth per microframe to work
+		  together.
+
+		Through this setting it is possible to raise the limit so that
+		the host controller would allow allocating more than 100
+		microseconds of periodic bandwidth per microframe.
+
+		Beware, non-standard modes are usually not thoroughly tested by
+		hardware designers, and the hardware can malfunction when this
+		setting differ from default 100.
+
+What:		/sys/module/*/{coresize,initsize}
+Date:		Jan 2012
+KernelVersion:	3.3
+Contact:	Kay Sievers <kay.sievers@vrfy.org>
+Description:	Module size in bytes.
+
+What:		/sys/module/*/initstate
+Date:		Nov 2006
+KernelVersion:	2.6.19
+Contact:	Kay Sievers <kay.sievers@vrfy.org>
+Description:	Show the initialization state(live, coming, going) of
+		the module.
+
+What:		/sys/module/*/import_ns
+Date:		January 2026
+KernelVersion:	7.1
+Contact:	linux-modules@vger.kernel.org
+Description:	List of symbol namespaces imported by this module via
+		MODULE_IMPORT_NS(). Each namespace appears on a separate line.
+		This file only exists for modules that import at least one
+		namespace.
+
+What:		/sys/module/*/taint
+Date:		Jan 2012
+KernelVersion:	3.3
+Contact:	Kay Sievers <kay.sievers@vrfy.org>
+Description:	Module taint flags:
+			==  =====================
+			P   proprietary module
+			O   out-of-tree module
+			F   force-loaded module
+			C   staging driver module
+			E   unsigned module
+			K   livepatch module
+			N   in-kernel test module
+			==  =====================
+
+What:		/sys/module/grant_table/parameters/free_per_iteration
+Date:		July 2023
+KernelVersion:	6.5 but backported to all supported stable branches
+Contact:	Xen developer discussion <xen-devel@lists.xenproject.org>
+Description:	Read and write number of grant entries to attempt to free per iteration.
+
+		Note: Future versions of Xen and Linux may provide a better
+		interface for controlling the rate of deferred grant reclaim
+		or may not need it at all.
+Users:		Qubes OS (https://www.qubes-os.org)