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>

3 files changed, 157 insertions, 0 deletions

diff --git a/Documentation/admin-guide/auxdisplay/cfag12864b.rst b/Documentation/admin-guide/auxdisplay/cfag12864b.rst
new file mode 100644
index 000000000..da385d851
--- /dev/null
+++ b/Documentation/admin-guide/auxdisplay/cfag12864b.rst
@@ -0,0 +1,98 @@
+===================================
+cfag12864b LCD Driver Documentation
+===================================
+
+:License:		GPLv2
+:Author & Maintainer:	Miguel Ojeda <ojeda@kernel.org>
+:Date:			2006-10-27
+
+
+
+.. INDEX
+
+	1. DRIVER INFORMATION
+	2. DEVICE INFORMATION
+	3. WIRING
+	4. USERSPACE PROGRAMMING
+
+1. Driver Information
+---------------------
+
+This driver supports a cfag12864b LCD.
+
+
+2. Device Information
+---------------------
+
+:Manufacturer:	Crystalfontz
+:Device Name:	Crystalfontz 12864b LCD Series
+:Device Code:	cfag12864b
+:Webpage:	http://www.crystalfontz.com
+:Device Webpage: http://www.crystalfontz.com/products/12864b/
+:Type:		LCD (Liquid Crystal Display)
+:Width:		128
+:Height:	64
+:Colors:	2 (B/N)
+:Controller:	ks0108
+:Controllers:	2
+:Pages:		8 each controller
+:Addresses:	64 each page
+:Data size:	1 byte each address
+:Memory size:	2 * 8 * 64 * 1 = 1024 bytes = 1 Kbyte
+
+
+3. Wiring
+---------
+
+The cfag12864b LCD Series don't have official wiring.
+
+The common wiring is done to the parallel port as shown::
+
+  Parallel Port                          cfag12864b
+
+    Name Pin#                            Pin# Name
+
+  Strobe ( 1)------------------------------(17) Enable
+  Data 0 ( 2)------------------------------( 4) Data 0
+  Data 1 ( 3)------------------------------( 5) Data 1
+  Data 2 ( 4)------------------------------( 6) Data 2
+  Data 3 ( 5)------------------------------( 7) Data 3
+  Data 4 ( 6)------------------------------( 8) Data 4
+  Data 5 ( 7)------------------------------( 9) Data 5
+  Data 6 ( 8)------------------------------(10) Data 6
+  Data 7 ( 9)------------------------------(11) Data 7
+         (10)                      [+5v]---( 1) Vdd
+         (11)                      [GND]---( 2) Ground
+         (12)                      [+5v]---(14) Reset
+         (13)                      [GND]---(15) Read / Write
+    Line (14)------------------------------(13) Controller Select 1
+         (15)
+    Init (16)------------------------------(12) Controller Select 2
+  Select (17)------------------------------(16) Data / Instruction
+  Ground (18)---[GND]              [+5v]---(19) LED +
+  Ground (19)---[GND]
+  Ground (20)---[GND]              E    A             Values:
+  Ground (21)---[GND]       [GND]---[P1]---(18) Vee    - R = Resistor = 22 ohm
+  Ground (22)---[GND]                |                 - P1 = Preset = 10 Kohm
+  Ground (23)---[GND]       ----   S ------( 3) V0     - P2 = Preset = 1 Kohm
+  Ground (24)---[GND]       |  |
+  Ground (25)---[GND] [GND]---[P2]---[R]---(20) LED -
+
+
+4. Userspace Programming
+------------------------
+
+The cfag12864bfb describes a framebuffer device (/dev/fbX).
+
+It has a size of 1024 bytes = 1 Kbyte.
+Each bit represents one pixel. If the bit is high, the pixel will
+turn on. If the pixel is low, the pixel will turn off.
+
+You can use the framebuffer as a file: fopen, fwrite, fclose...
+Although the LCD won't get updated until the next refresh time arrives.
+
+Also, you can mmap the framebuffer: open & mmap, munmap & close...
+which is the best option for most uses.
+
+Check samples/auxdisplay/cfag12864b-example.c
+for a real working userspace complete program with usage examples.
diff --git a/Documentation/admin-guide/auxdisplay/index.rst b/Documentation/admin-guide/auxdisplay/index.rst
new file mode 100644
index 000000000..31eae0825
--- /dev/null
+++ b/Documentation/admin-guide/auxdisplay/index.rst
@@ -0,0 +1,9 @@
+=========================
+Auxiliary Display Support
+=========================
+
+.. toctree::
+    :maxdepth: 1
+
+    ks0108.rst
+    cfag12864b.rst
diff --git a/Documentation/admin-guide/auxdisplay/ks0108.rst b/Documentation/admin-guide/auxdisplay/ks0108.rst
new file mode 100644
index 000000000..a7d3fe509
--- /dev/null
+++ b/Documentation/admin-guide/auxdisplay/ks0108.rst
@@ -0,0 +1,50 @@
+==========================================
+ks0108 LCD Controller Driver Documentation
+==========================================
+
+:License:		GPLv2
+:Author & Maintainer:	Miguel Ojeda <ojeda@kernel.org>
+:Date:			2006-10-27
+
+
+
+.. INDEX
+
+	1. DRIVER INFORMATION
+	2. DEVICE INFORMATION
+	3. WIRING
+
+
+1. Driver Information
+---------------------
+
+This driver supports the ks0108 LCD controller.
+
+
+2. Device Information
+---------------------
+
+:Manufacturer:	Samsung
+:Device Name:	KS0108 LCD Controller
+:Device Code:	ks0108
+:Webpage:	-
+:Device Webpage: -
+:Type:		LCD Controller (Liquid Crystal Display Controller)
+:Width:		64
+:Height:	64
+:Colors:	2 (B/N)
+:Pages:		8
+:Addresses:	64 each page
+:Data size:	1 byte each address
+:Memory size:	8 * 64 * 1 = 512 bytes
+
+
+3. Wiring
+---------
+
+The driver supports data parallel port wiring.
+
+If you aren't building LCD related hardware, you should check
+your LCD specific wiring information in the same folder.
+
+For example, check Documentation/admin-guide/auxdisplay/cfag12864b.rst