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, 167 insertions, 0 deletions

diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
new file mode 100644
index 000000000..9ba45e5b3
--- /dev/null
+++ b/scripts/Makefile.modinst
@@ -0,0 +1,167 @@
+# SPDX-License-Identifier: GPL-2.0
+# ==========================================================================
+# Installing modules
+# ==========================================================================
+
+PHONY := __modinst
+__modinst:
+
+include $(objtree)/include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+
+install-y :=
+
+ifeq ($(KBUILD_EXTMOD)$(sign-only),)
+
+# remove the old directory and symlink
+$(shell rm -fr $(MODLIB)/kernel $(MODLIB)/build)
+
+install-$(CONFIG_MODULES) += $(addprefix $(MODLIB)/, build modules.order)
+
+$(MODLIB)/build: FORCE
+	$(call cmd,symlink)
+
+quiet_cmd_symlink = SYMLINK $@
+      cmd_symlink = ln -s $(CURDIR) $@
+
+$(MODLIB)/modules.order: modules.order FORCE
+	$(call cmd,install_modorder)
+
+quiet_cmd_install_modorder = INSTALL $@
+      cmd_install_modorder = sed 's:^\(.*\)\.o$$:kernel/\1.ko:' $< > $@
+
+# Install modules.builtin(.modinfo,.ranges) even when CONFIG_MODULES is disabled.
+install-y += $(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo)
+
+install-$(CONFIG_BUILTIN_MODULE_RANGES) += $(MODLIB)/modules.builtin.ranges
+
+$(addprefix $(MODLIB)/, modules.builtin modules.builtin.modinfo modules.builtin.ranges): $(MODLIB)/%: % FORCE
+	$(call cmd,install)
+
+endif
+
+modules := $(call read-file, modules.order)
+
+ifeq ($(KBUILD_EXTMOD),)
+dst := $(MODLIB)/kernel
+else
+INSTALL_MOD_DIR ?= updates
+dst := $(MODLIB)/$(INSTALL_MOD_DIR)
+endif
+
+$(foreach x, % :, $(if $(findstring $x, $(dst)), \
+	$(error module installation path cannot contain '$x')))
+
+suffix-y				:=
+ifdef CONFIG_MODULE_COMPRESS_ALL
+suffix-$(CONFIG_MODULE_COMPRESS_GZIP)	:= .gz
+suffix-$(CONFIG_MODULE_COMPRESS_XZ)	:= .xz
+suffix-$(CONFIG_MODULE_COMPRESS_ZSTD)	:= .zst
+endif
+
+modules := $(patsubst %.o, $(dst)/%.ko$(suffix-y), $(modules))
+install-$(CONFIG_MODULES) += $(modules)
+
+__modinst: $(install-y)
+	@:
+
+#
+# Installation
+#
+quiet_cmd_install = INSTALL $@
+      cmd_install = cp $< $@
+
+# Strip
+#
+# INSTALL_MOD_STRIP, if defined, will cause modules to be stripped after they
+# are installed. If INSTALL_MOD_STRIP is '1', then the default option
+# --strip-debug will be used. Otherwise, INSTALL_MOD_STRIP value will be used
+# as the options to the strip command.
+ifdef INSTALL_MOD_STRIP
+
+ifeq ($(INSTALL_MOD_STRIP),1)
+strip-option := --strip-debug
+else
+strip-option := $(INSTALL_MOD_STRIP)
+endif
+
+quiet_cmd_strip = STRIP   $@
+      cmd_strip = $(STRIP) $(strip-option) $@
+
+else
+
+quiet_cmd_strip =
+      cmd_strip = :
+
+endif
+
+#
+# Signing
+# Don't stop modules_install even if we can't sign external modules.
+#
+ifeq ($(filter pkcs11:%, $(CONFIG_MODULE_SIG_KEY)),)
+sig-key := $(if $(wildcard $(CONFIG_MODULE_SIG_KEY)),,$(objtree)/)$(CONFIG_MODULE_SIG_KEY)
+else
+sig-key := $(CONFIG_MODULE_SIG_KEY)
+endif
+quiet_cmd_sign = SIGN    $@
+      cmd_sign = $(objtree)/scripts/sign-file $(CONFIG_MODULE_SIG_HASH) "$(sig-key)" $(objtree)/certs/signing_key.x509 $@ \
+                 $(if $(KBUILD_EXTMOD),|| true)
+
+ifeq ($(sign-only),)
+
+# During modules_install, modules are signed only when CONFIG_MODULE_SIG_ALL=y.
+ifndef CONFIG_MODULE_SIG_ALL
+quiet_cmd_sign :=
+      cmd_sign := :
+endif
+
+# Create necessary directories
+$(foreach dir, $(sort $(dir $(install-y))), $(shell mkdir -p $(dir)))
+
+$(dst)/%.ko: %.ko FORCE
+	$(call cmd,install)
+	$(call cmd,strip)
+	$(call cmd,sign)
+
+ifdef CONFIG_MODULES
+__modinst: depmod
+
+PHONY += depmod
+depmod: $(install-y)
+	$(call cmd,depmod)
+
+quiet_cmd_depmod = DEPMOD  $(MODLIB)
+      cmd_depmod = $(srctree)/scripts/depmod.sh $(KERNELRELEASE)
+endif
+
+else
+
+$(dst)/%.ko: FORCE
+	$(call cmd,sign)
+
+endif
+
+#
+# Compression
+#
+quiet_cmd_gzip = GZIP    $@
+      cmd_gzip = $(KGZIP) -n -f $<
+quiet_cmd_xz = XZ      $@
+      cmd_xz = $(XZ) --check=crc32 --lzma2=dict=1MiB -f $<
+quiet_cmd_zstd = ZSTD    $@
+      cmd_zstd = $(ZSTD) --rm -f -q $<
+
+$(dst)/%.ko.gz: $(dst)/%.ko FORCE
+	$(call cmd,gzip)
+
+$(dst)/%.ko.xz: $(dst)/%.ko FORCE
+	$(call cmd,xz)
+
+$(dst)/%.ko.zst: $(dst)/%.ko FORCE
+	$(call cmd,zstd)
+
+PHONY += FORCE
+FORCE:
+
+.PHONY: $(PHONY)