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, 41 insertions, 0 deletions

diff --git a/include/net/mip6.h b/include/net/mip6.h
new file mode 100644
index 000000000..67cd7e508
--- /dev/null
+++ b/include/net/mip6.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C)2003-2006 Helsinki University of Technology
+ * Copyright (C)2003-2006 USAGI/WIDE Project
+ */
+/*
+ * Authors:
+ *	Noriaki TAKAMIYA @USAGI
+ *	Masahide NAKAMURA @USAGI
+ *	YOSHIFUJI Hideaki @USAGI
+ */
+#ifndef _NET_MIP6_H
+#define _NET_MIP6_H
+
+#include <linux/skbuff.h>
+#include <net/sock.h>
+
+/*
+ * Mobility Header
+ */
+struct ip6_mh {
+	__u8	ip6mh_proto;
+	__u8	ip6mh_hdrlen;
+	__u8	ip6mh_type;
+	__u8	ip6mh_reserved;
+	__u16	ip6mh_cksum;
+	/* Followed by type specific messages */
+	__u8	data[];
+} __packed;
+
+#define IP6_MH_TYPE_BRR		0   /* Binding Refresh Request */
+#define IP6_MH_TYPE_HOTI	1   /* HOTI Message   */
+#define IP6_MH_TYPE_COTI	2   /* COTI Message  */
+#define IP6_MH_TYPE_HOT		3   /* HOT Message   */
+#define IP6_MH_TYPE_COT		4   /* COT Message  */
+#define IP6_MH_TYPE_BU		5   /* Binding Update */
+#define IP6_MH_TYPE_BACK	6   /* Binding ACK */
+#define IP6_MH_TYPE_BERROR	7   /* Binding Error */
+#define IP6_MH_TYPE_MAX		IP6_MH_TYPE_BERROR
+
+#endif