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, 63 insertions, 0 deletions

diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
new file mode 100644
index 000000000..6ead00ec7
--- /dev/null
+++ b/scripts/Makefile.clean
@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: GPL-2.0
+# ==========================================================================
+# Cleaning up
+# ==========================================================================
+
+src := $(srcroot)/$(obj)
+
+PHONY := __clean
+__clean:
+
+include $(srctree)/scripts/Kbuild.include
+include $(kbuild-file)
+
+# Figure out what we need to build from the various variables
+# ==========================================================================
+
+subdir-ymn := $(sort $(subdir-y) $(subdir-m) $(subdir-) \
+		$(patsubst %/,%, $(filter %/, $(obj-y) $(obj-m) $(obj-))))
+
+# Add subdir path
+
+subdir-ymn	:= $(addprefix $(obj)/,$(subdir-ymn))
+
+# build a list of files to remove, usually relative to the current
+# directory
+
+__clean-files	:= \
+	$(clean-files) $(targets) $(hostprogs) $(userprogs) \
+	$(extra-y) $(extra-m) $(extra-) \
+	$(always-y) $(always-m) $(always-) \
+	$(hostprogs-always-y) $(hostprogs-always-m) $(hostprogs-always-) \
+	$(userprogs-always-y) $(userprogs-always-m) $(userprogs-always-)
+
+__clean-files   := $(filter-out $(no-clean-files), $(__clean-files))
+
+__clean-files   := $(wildcard $(addprefix $(obj)/, $(__clean-files)))
+
+# ==========================================================================
+
+# To make this rule robust against "Argument list too long" error,
+# remove $(obj)/ prefix, and restore it by a shell command.
+quiet_cmd_clean = CLEAN   $(obj)
+      cmd_clean = printf '$(obj)/%s ' $(patsubst $(obj)/%,%,$(__clean-files)) | xargs rm -rf
+
+__clean: $(subdir-ymn)
+ifneq ($(strip $(__clean-files)),)
+	$(call cmd,clean)
+endif
+	@:
+
+
+# ===========================================================================
+# Generic stuff
+# ===========================================================================
+
+# Descending
+# ---------------------------------------------------------------------------
+
+PHONY += $(subdir-ymn)
+$(subdir-ymn):
+	$(Q)$(MAKE) $(clean)=$@
+
+.PHONY: $(PHONY)