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, 37 insertions, 0 deletions

diff --git a/net/ethtool/bitset.h b/net/ethtool/bitset.h
new file mode 100644
index 000000000..07bc547d4
--- /dev/null
+++ b/net/ethtool/bitset.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _NET_ETHTOOL_BITSET_H
+#define _NET_ETHTOOL_BITSET_H
+
+#include <linux/ethtool.h>
+#include <linux/netlink.h>
+
+#define ETHNL_MAX_BITSET_SIZE S16_MAX
+
+typedef const char (*const ethnl_string_array_t)[ETH_GSTRING_LEN];
+
+int ethnl_bitset_is_compact(const struct nlattr *bitset, bool *compact);
+int ethnl_bitset_size(const unsigned long *val, const unsigned long *mask,
+		      unsigned int nbits, ethnl_string_array_t names,
+		      bool compact);
+int ethnl_bitset32_size(const u32 *val, const u32 *mask, unsigned int nbits,
+			ethnl_string_array_t names, bool compact);
+int ethnl_put_bitset(struct sk_buff *skb, int attrtype,
+		     const unsigned long *val, const unsigned long *mask,
+		     unsigned int nbits, ethnl_string_array_t names,
+		     bool compact);
+int ethnl_put_bitset32(struct sk_buff *skb, int attrtype, const u32 *val,
+		       const u32 *mask, unsigned int nbits,
+		       ethnl_string_array_t names, bool compact);
+int ethnl_update_bitset(unsigned long *bitmap, unsigned int nbits,
+			const struct nlattr *attr, ethnl_string_array_t names,
+			struct netlink_ext_ack *extack, bool *mod);
+int ethnl_update_bitset32(u32 *bitmap, unsigned int nbits,
+			  const struct nlattr *attr, ethnl_string_array_t names,
+			  struct netlink_ext_ack *extack, bool *mod);
+int ethnl_parse_bitset(unsigned long *val, unsigned long *mask,
+		       unsigned int nbits, const struct nlattr *attr,
+		       ethnl_string_array_t names,
+		       struct netlink_ext_ack *extack);
+
+#endif /* _NET_ETHTOOL_BITSET_H */