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, 32 insertions, 0 deletions

diff --git a/security/keys/Makefile b/security/keys/Makefile
new file mode 100644
index 000000000..5f40807f0
--- /dev/null
+++ b/security/keys/Makefile
@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for key management
+#
+
+#
+# Core
+#
+obj-y := \
+	gc.o \
+	key.o \
+	keyring.o \
+	keyctl.o \
+	permission.o \
+	process_keys.o \
+	request_key.o \
+	request_key_auth.o \
+	user_defined.o
+compat-obj-$(CONFIG_KEY_DH_OPERATIONS) += compat_dh.o
+obj-$(CONFIG_COMPAT) += compat.o $(compat-obj-y)
+obj-$(CONFIG_PROC_FS) += proc.o
+obj-$(CONFIG_SYSCTL) += sysctl.o
+obj-$(CONFIG_PERSISTENT_KEYRINGS) += persistent.o
+obj-$(CONFIG_KEY_DH_OPERATIONS) += dh.o
+obj-$(CONFIG_ASYMMETRIC_KEY_TYPE) += keyctl_pkey.o
+
+#
+# Key types
+#
+obj-$(CONFIG_BIG_KEYS) += big_key.o
+obj-$(CONFIG_TRUSTED_KEYS) += trusted-keys/
+obj-$(CONFIG_ENCRYPTED_KEYS) += encrypted-keys/