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, 55 insertions, 0 deletions

diff --git a/tools/perf/python/tracepoint.py b/tools/perf/python/tracepoint.py
new file mode 100755
index 000000000..15b0c8268
--- /dev/null
+++ b/tools/perf/python/tracepoint.py
@@ -0,0 +1,55 @@
+#! /usr/bin/env python
+# SPDX-License-Identifier: GPL-2.0
+# -*- python -*-
+# -*- coding: utf-8 -*-
+
+import perf
+
+def change_proctitle():
+    try:
+        import setproctitle
+        setproctitle.setproctitle("tracepoint.py")
+    except:
+        print("Install the setproctitle python package to help with top and friends")
+
+def main():
+    change_proctitle()
+    cpus    = perf.cpu_map()
+    threads = perf.thread_map(-1)
+    evlist = perf.parse_events("sched:sched_switch", cpus, threads)
+    # Disable tracking of mmaps and similar that are unnecessary.
+    for ev in evlist:
+        ev.tracking = False
+    # Configure evsels with default record options.
+    evlist.config()
+    # Simplify the sample_type and read_format of evsels
+    for ev in evlist:
+        ev.sample_type = ev.sample_type & ~perf.SAMPLE_IP
+        ev.read_format = 0
+
+    evlist.open()
+    evlist.mmap()
+    evlist.enable();
+
+    while True:
+        evlist.poll(timeout = -1)
+        for cpu in cpus:
+            event = evlist.read_on_cpu(cpu)
+            if not event:
+                continue
+
+            if not isinstance(event, perf.sample_event):
+                continue
+
+            print("time %u prev_comm=%s prev_pid=%d prev_prio=%d prev_state=0x%x ==> next_comm=%s next_pid=%d next_prio=%d" % (
+                   event.sample_time,
+                   event.prev_comm,
+                   event.prev_pid,
+                   event.prev_prio,
+                   event.prev_state,
+                   event.next_comm,
+                   event.next_pid,
+                   event.next_prio))
+
+if __name__ == '__main__':
+    main()