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, 97 insertions, 0 deletions

diff --git a/scripts/package/debian/rules b/scripts/package/debian/rules
new file mode 100755
index 000000000..a417a7f8b
--- /dev/null
+++ b/scripts/package/debian/rules
@@ -0,0 +1,97 @@
+#!/usr/bin/make -f
+# SPDX-License-Identifier: GPL-2.0-only
+
+# in case debian/rules is executed directly
+export DEB_RULES_REQUIRES_ROOT := no
+
+include debian/rules.vars
+
+ifneq (,$(filter-out parallel=1,$(filter parallel=%,$(DEB_BUILD_OPTIONS))))
+    NUMJOBS = $(patsubst parallel=%,%,$(filter parallel=%,$(DEB_BUILD_OPTIONS)))
+    MAKEFLAGS += -j$(NUMJOBS)
+endif
+
+# When KBUILD_VERBOSE is undefined (presumably you are directly working with
+# the debianized tree), show verbose logs unless DEB_BUILD_OPTION=terse is set.
+ifeq ($(origin KBUILD_VERBOSE),undefined)
+    ifeq (,$(filter terse,$(DEB_BUILD_OPTIONS)))
+        export KBUILD_VERBOSE := 1
+    else
+        Q := @
+    endif
+endif
+
+revision = $(shell dpkg-parsechangelog -S Version | sed -n 's/.*-//p')
+CROSS_COMPILE ?= $(filter-out $(DEB_BUILD_GNU_TYPE)-, $(DEB_HOST_GNU_TYPE)-)
+make-opts = ARCH=$(ARCH) KERNELRELEASE=$(KERNELRELEASE) \
+    $(addprefix KBUILD_BUILD_VERSION=,$(revision)) \
+    $(addprefix CROSS_COMPILE=,$(CROSS_COMPILE))
+
+binary-targets := $(addprefix binary-, image image-dbg headers libc-dev)
+
+all-packages = $(shell dh_listpackages)
+image-package = $(filter linux-image-% user-%, $(filter-out %-dbg, $(all-packages)))
+image-dbg-package = $(filter %-dbg, $(all-packages))
+libc-dev-package = $(filter linux-libc-dev, $(all-packages))
+headers-package = $(filter linux-headers-%, $(all-packages))
+
+mk-files = $(patsubst binary-%,debian/%.files,$1)
+package = $($(@:binary-%=%-package))
+
+# DH_OPTION is an environment variable common for all debhelper commands.
+# We could 'export' it, but here it is passed from the command line to clarify
+# which package is being processed in the build log.
+DH_OPTIONS = -p$(package)
+
+# Note: future removal of KDEB_COMPRESS
+# dpkg-deb >= 1.21.10 supports the DPKG_DEB_COMPRESSOR_TYPE environment
+# variable, which provides the same functionality as KDEB_COMPRESS. The
+# KDEB_COMPRESS variable will be removed in the future.
+define binary
+	$(Q)dh_testdir $(DH_OPTIONS)
+	$(Q)dh_testroot $(DH_OPTIONS)
+	$(Q)dh_prep $(DH_OPTIONS)
+	$(Q)+$(MAKE) $(make-opts) run-command KBUILD_RUN_COMMAND='+$$(srctree)/scripts/package/builddeb $(package)'
+	$(Q)dh_installdocs $(DH_OPTIONS)
+	$(Q)dh_installchangelogs $(DH_OPTIONS)
+	$(Q)dh_compress $(DH_OPTIONS)
+	$(Q)dh_fixperms $(DH_OPTIONS)
+	$(Q)dh_gencontrol $(DH_OPTIONS) -- -f$(call mk-files,$@)
+	$(Q)dh_md5sums $(DH_OPTIONS)
+	$(Q)dh_builddeb $(DH_OPTIONS) -- $(addprefix -Z,$(KDEB_COMPRESS))
+endef
+
+.PHONY: $(binary-targets)
+$(binary-targets): build-arch
+	$(Q)truncate -s0 $(call mk-files,$@)
+	$(if $(package),$(binary))
+
+.PHONY: binary binary-indep binary-arch
+binary: binary-arch binary-indep
+binary-indep: build-indep
+binary-arch: $(binary-targets)
+	$(Q)cat $(call mk-files,$^) > debian/files
+
+.PHONY: build build-indep build-arch
+build: build-arch build-indep
+build-indep:
+build-arch:
+	$(Q)$(MAKE) $(make-opts) olddefconfig
+	$(Q)$(MAKE) $(make-opts) $(if $(filter um,$(ARCH)),,headers) all
+
+.PHONY: clean
+clean:
+	$(Q)dh_clean
+	$(Q)rm -rf debian/deb-env.vars* debian/*.files
+	$(Q)$(MAKE) ARCH=$(ARCH) clean
+
+# If DEB_HOST_ARCH is empty, it is likely that debian/rules was executed
+# directly. Run 'dpkg-architecture --print-set --print-format=make' to
+# generate a makefile construct that exports all DEB_* variables.
+ifndef DEB_HOST_ARCH
+include debian/deb-env.vars
+
+debian/deb-env.vars:
+	$(Q)dpkg-architecture -a$$(cat debian/arch) --print-set --print-format=make > $@.tmp
+	$(Q)mv $@.tmp $@
+endif