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, 46 insertions, 0 deletions

diff --git a/arch/alpha/lib/Makefile b/arch/alpha/lib/Makefile
new file mode 100644
index 000000000..84046e730
--- /dev/null
+++ b/arch/alpha/lib/Makefile
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for alpha-specific library files..
+#
+
+asflags-y := $(KBUILD_CFLAGS)
+
+# Many of these routines have implementations tuned for ev6.
+# Choose them iff we're targeting ev6 specifically.
+ev6-$(CONFIG_ALPHA_EV6) := ev6-
+
+# Several make use of the cttz instruction introduced in ev67.
+ev67-$(CONFIG_ALPHA_EV67) := ev67-
+
+lib-y =	__divqu.o __remqu.o __divlu.o __remlu.o \
+	udiv-qrnnd.o \
+	udelay.o \
+	$(ev6-y)memset.o \
+	$(ev6-y)memcpy.o \
+	memmove.o \
+	checksum.o \
+	csum_partial_copy.o \
+	$(ev67-y)strlen.o \
+	stycpy.o \
+	styncpy.o \
+	$(ev67-y)strchr.o \
+	$(ev67-y)strrchr.o \
+	$(ev6-y)memchr.o \
+	$(ev6-y)copy_user.o \
+	$(ev6-y)clear_user.o \
+	$(ev6-y)csum_ipv6_magic.o \
+	$(ev6-y)clear_page.o \
+	$(ev6-y)copy_page.o \
+	fpreg.o \
+	callback_srm.o srm_puts.o srm_printk.o \
+	fls.o
+
+# The division routines are built from single source, with different defines.
+AFLAGS___divqu.o = -DDIV
+AFLAGS___remqu.o =       -DREM
+AFLAGS___divlu.o = -DDIV       -DINTSIZE
+AFLAGS___remlu.o =       -DREM -DINTSIZE
+
+$(addprefix $(obj)/,__divqu.o __remqu.o __divlu.o __remlu.o): \
+						$(src)/$(ev6-y)divide.S FORCE
+	$(call if_changed_rule,as_o_S)