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, 60 insertions, 0 deletions

diff --git a/arch/alpha/Makefile b/arch/alpha/Makefile
new file mode 100644
index 000000000..35445ff2e
--- /dev/null
+++ b/arch/alpha/Makefile
@@ -0,0 +1,60 @@
+#
+# alpha/Makefile
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 1994 by Linus Torvalds
+#
+
+NM := $(NM) -B
+
+LDFLAGS_vmlinux	:= -static -N #-relax
+CHECKFLAGS	+= -D__alpha__
+cflags-y	:= -pipe -mno-fp-regs -ffixed-8
+cflags-y	+= $(call cc-option, -fno-jump-tables)
+
+cpuflags-$(CONFIG_ALPHA_EV56)		:= -mcpu=ev56
+cpuflags-$(CONFIG_ALPHA_POLARIS)	:= -mcpu=pca56
+cpuflags-$(CONFIG_ALPHA_SX164)		:= -mcpu=pca56
+cpuflags-$(CONFIG_ALPHA_EV6)		:= -mcpu=ev6
+cpuflags-$(CONFIG_ALPHA_EV67)		:= -mcpu=ev67
+# If GENERIC, make sure to turn off any instruction set extensions that
+# the host compiler might have on by default.
+cpuflags-$(CONFIG_ALPHA_GENERIC)	:= -mcpu=ev56 -mtune=ev6
+
+cflags-y				+= $(cpuflags-y)
+
+
+# For TSUNAMI, we must have the assembler not emulate our instructions.
+# The same is true for IRONGATE, POLARIS, PYXIS.
+# BWX is most important, but we don't really want any emulation ever.
+KBUILD_CFLAGS += $(cflags-y) -Wa,-mev6
+
+libs-y				+= arch/alpha/lib/
+
+# export what is needed by arch/alpha/boot/Makefile
+LIBS_Y := $(patsubst %/, %/lib.a, $(libs-y))
+export LIBS_Y
+
+boot := arch/alpha/boot
+
+#Default target when executing make with no arguments
+all boot: $(boot)/vmlinux.gz
+
+$(boot)/vmlinux.gz: vmlinux
+	$(Q)$(MAKE) $(build)=$(boot) $@
+
+bootimage bootpfile bootpzfile: vmlinux
+	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+
+archheaders:
+	$(Q)$(MAKE) $(build)=arch/alpha/kernel/syscalls all
+
+define archhelp
+  echo '* boot		- Compressed kernel image (arch/alpha/boot/vmlinux.gz)'
+  echo '  bootimage	- SRM bootable image (arch/alpha/boot/bootimage)'
+  echo '  bootpfile	- BOOTP bootable image (arch/alpha/boot/bootpfile)'
+  echo '  bootpzfile	- compressed kernel BOOTP image (arch/alpha/boot/bootpzfile)'
+endef