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, 39 insertions, 0 deletions

diff --git a/include/net/dcbevent.h b/include/net/dcbevent.h
new file mode 100644
index 000000000..02700262f
--- /dev/null
+++ b/include/net/dcbevent.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2010, Intel Corporation.
+ *
+ * Author: John Fastabend <john.r.fastabend@intel.com>
+ */
+
+#ifndef _DCB_EVENT_H
+#define _DCB_EVENT_H
+
+struct notifier_block;
+
+enum dcbevent_notif_type {
+	DCB_APP_EVENT = 1,
+};
+
+#ifdef CONFIG_DCB
+int register_dcbevent_notifier(struct notifier_block *nb);
+int unregister_dcbevent_notifier(struct notifier_block *nb);
+int call_dcbevent_notifiers(unsigned long val, void *v);
+#else
+static inline int
+register_dcbevent_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int unregister_dcbevent_notifier(struct notifier_block *nb)
+{
+	return 0;
+}
+
+static inline int call_dcbevent_notifiers(unsigned long val, void *v)
+{
+	return 0;
+}
+#endif /* CONFIG_DCB */
+
+#endif