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>

3 files changed, 51 insertions, 0 deletions

diff --git a/tools/testing/selftests/rust/Makefile b/tools/testing/selftests/rust/Makefile
new file mode 100644
index 000000000..fce1584d3
--- /dev/null
+++ b/tools/testing/selftests/rust/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+TEST_PROGS += test_probe_samples.sh
+
+include ../lib.mk
diff --git a/tools/testing/selftests/rust/config b/tools/testing/selftests/rust/config
new file mode 100644
index 000000000..5f942b5c8
--- /dev/null
+++ b/tools/testing/selftests/rust/config
@@ -0,0 +1,6 @@
+# CONFIG_GCC_PLUGINS is not set
+CONFIG_RUST=y
+CONFIG_SAMPLES=y
+CONFIG_SAMPLES_RUST=y
+CONFIG_SAMPLE_RUST_MINIMAL=m
+CONFIG_SAMPLE_RUST_PRINT=m
diff --git a/tools/testing/selftests/rust/test_probe_samples.sh b/tools/testing/selftests/rust/test_probe_samples.sh
new file mode 100755
index 000000000..ad0397e49
--- /dev/null
+++ b/tools/testing/selftests/rust/test_probe_samples.sh
@@ -0,0 +1,41 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (c) 2023 Collabora Ltd
+#
+# This script tests whether the rust sample modules can
+# be added and removed correctly.
+#
+DIR="$(dirname "$(readlink -f "$0")")"
+
+KTAP_HELPERS="${DIR}/../kselftest/ktap_helpers.sh"
+if [ -e "$KTAP_HELPERS" ]; then
+    source "$KTAP_HELPERS"
+else
+    echo "$KTAP_HELPERS file not found [SKIP]"
+    exit 4
+fi
+
+rust_sample_modules=("rust_minimal" "rust_print")
+
+ktap_print_header
+
+for sample in "${rust_sample_modules[@]}"; do
+    if ! /sbin/modprobe -n -q "$sample"; then
+        ktap_skip_all "module $sample is not found in /lib/modules/$(uname -r)"
+        exit "$KSFT_SKIP"
+    fi
+done
+
+ktap_set_plan "${#rust_sample_modules[@]}"
+
+for sample in "${rust_sample_modules[@]}"; do
+    if /sbin/modprobe -q "$sample"; then
+        /sbin/modprobe -q -r "$sample"
+        ktap_test_pass "$sample"
+    else
+        ktap_test_fail "$sample"
+    fi
+done
+
+ktap_finished