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>

2 files changed, 42 insertions, 0 deletions

diff --git a/Documentation/PCI/controller/index.rst b/Documentation/PCI/controller/index.rst
new file mode 100644
index 000000000..c2ce9ccdc
--- /dev/null
+++ b/Documentation/PCI/controller/index.rst
@@ -0,0 +1,10 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================================
+PCI Native Host Bridge and Endpoint Drivers
+===========================================
+
+.. toctree::
+   :maxdepth: 2
+
+   rcar-pcie-firmware
diff --git a/Documentation/PCI/controller/rcar-pcie-firmware.rst b/Documentation/PCI/controller/rcar-pcie-firmware.rst
new file mode 100644
index 000000000..67d3bf66e
--- /dev/null
+++ b/Documentation/PCI/controller/rcar-pcie-firmware.rst
@@ -0,0 +1,32 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================================
+Firmware of PCIe controller for Renesas R-Car V4H
+=================================================
+
+Renesas R-Car V4H (r8a779g0) has a PCIe controller, requiring a specific
+firmware download during startup.
+
+However, Renesas currently cannot distribute the firmware free of charge.
+
+The firmware file "104_PCIe_fw_addr_data_ver1.05.txt" (note that the file name
+might be different between different datasheet revisions) can be found in the
+datasheet encoded as text, and as such, the file's content must be converted
+back to binary form. This can be achieved using the following example script:
+
+.. code-block:: sh
+
+	$ awk '/^\s*0x[0-9A-Fa-f]{4}\s+0x[0-9A-Fa-f]{4}/ { print substr($2,5,2) substr($2,3,2) }' \
+		104_PCIe_fw_addr_data_ver1.05.txt | \
+			xxd -p -r > rcar_gen4_pcie.bin
+
+Once the text content has been converted into a binary firmware file, verify
+its checksum as follows:
+
+.. code-block:: sh
+
+	$ sha1sum rcar_gen4_pcie.bin
+	1d0bd4b189b4eb009f5d564b1f93a79112994945  rcar_gen4_pcie.bin
+
+The resulting binary file called "rcar_gen4_pcie.bin" should be placed in the
+"/lib/firmware" directory before the driver runs.