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/net/openvswitch/drop.h b/net/openvswitch/drop.h
new file mode 100644
index 000000000..cedf9b7b5
--- /dev/null
+++ b/net/openvswitch/drop.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * OpenvSwitch drop reason list.
+ */
+
+#ifndef OPENVSWITCH_DROP_H
+#define OPENVSWITCH_DROP_H
+#include <linux/skbuff.h>
+#include <net/dropreason.h>
+
+#define OVS_DROP_REASONS(R)			\
+	R(OVS_DROP_LAST_ACTION)		        \
+	R(OVS_DROP_ACTION_ERROR)		\
+	R(OVS_DROP_EXPLICIT)			\
+	R(OVS_DROP_EXPLICIT_WITH_ERROR)		\
+	R(OVS_DROP_METER)			\
+	R(OVS_DROP_RECURSION_LIMIT)		\
+	R(OVS_DROP_DEFERRED_LIMIT)		\
+	R(OVS_DROP_FRAG_L2_TOO_LONG)		\
+	R(OVS_DROP_FRAG_INVALID_PROTO)		\
+	R(OVS_DROP_CONNTRACK)			\
+	R(OVS_DROP_IP_TTL)			\
+	/* deliberate comment for trailing \ */
+
+enum ovs_drop_reason {
+	__OVS_DROP_REASON = SKB_DROP_REASON_SUBSYS_OPENVSWITCH <<
+				SKB_DROP_REASON_SUBSYS_SHIFT,
+#define ENUM(x) x,
+	OVS_DROP_REASONS(ENUM)
+#undef ENUM
+
+	OVS_DROP_MAX,
+};
+
+static inline void
+ovs_kfree_skb_reason(struct sk_buff *skb, enum ovs_drop_reason reason)
+{
+	kfree_skb_reason(skb, (u32)reason);
+}
+
+#endif /* OPENVSWITCH_DROP_H */