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, 30 insertions, 0 deletions

diff --git a/tools/bootconfig/Makefile b/tools/bootconfig/Makefile
new file mode 100644
index 000000000..90eb47c9d
--- /dev/null
+++ b/tools/bootconfig/Makefile
@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for bootconfig command
+include ../scripts/Makefile.include
+
+bindir ?= /usr/bin
+
+ifeq ($(srctree),)
+srctree := $(patsubst %/,%,$(dir $(CURDIR)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+endif
+
+LIBSRC = $(srctree)/lib/bootconfig.c $(srctree)/include/linux/bootconfig.h
+override CFLAGS += -Wall -g -I$(CURDIR)/include
+
+ALL_TARGETS := bootconfig
+ALL_PROGRAMS := $(patsubst %,$(OUTPUT)%,$(ALL_TARGETS))
+
+all: $(ALL_PROGRAMS) test
+
+$(OUTPUT)bootconfig: main.c include/linux/bootconfig.h $(LIBSRC)
+	$(CC) $(filter %.c,$^) $(CFLAGS) $(LDFLAGS) -o $@
+
+test: $(ALL_PROGRAMS) test-bootconfig.sh
+	./test-bootconfig.sh $(OUTPUT)
+
+install: $(ALL_PROGRAMS)
+	install $(OUTPUT)bootconfig $(DESTDIR)$(bindir)
+
+clean:
+	$(RM) -f $(OUTPUT)*.o $(ALL_PROGRAMS)