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, 96 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-switchtec b/Documentation/ABI/testing/sysfs-class-switchtec
new file mode 100644
index 000000000..76c7a661a
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-switchtec
@@ -0,0 +1,96 @@
+switchtec - Microsemi Switchtec PCI Switch Management Endpoint
+
+For details on this subsystem look at Documentation/driver-api/switchtec.rst.
+
+What: 		/sys/class/switchtec
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	The switchtec class subsystem folder.
+		Each registered switchtec driver is represented by a switchtecX
+		subfolder (X being an integer >= 0).
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/component_id
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Component identifier as stored in the hardware (eg. PM8543)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/component_revision
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Component revision stored in the hardware (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/component_vendor
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Component vendor as stored in the hardware (eg. MICROSEM)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/device_version
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Device version as stored in the hardware (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/fw_version
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Currently running firmware version (read only)
+Values: 	integer (in hexadecimal).
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/partition
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Partition number for this device in the switch (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/partition_count
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Total number of partitions in the switch (read only)
+Values: 	integer.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/product_id
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Product identifier as stored in the hardware (eg. PSX 48XG3)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/product_revision
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Product revision stored in the hardware (eg. RevB)
+		(read only)
+Values: 	arbitrary string.
+
+
+What:		/sys/class/switchtec/switchtec[0-9]+/product_vendor
+Date:		05-Jan-2017
+KernelVersion:	v4.11
+Contact:	Logan Gunthorpe <logang@deltatee.com>
+Description:	Product vendor as stored in the hardware (eg. MICROSEM)
+		(read only)
+Values: 	arbitrary string.