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, 28 insertions, 0 deletions

diff --git a/include/net/ipconfig.h b/include/net/ipconfig.h
new file mode 100644
index 000000000..8276897d0
--- /dev/null
+++ b/include/net/ipconfig.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  Copyright (C) 1997 Martin Mares
+ *
+ *  Automatic IP Layer Configuration
+ */
+
+/* The following are initdata: */
+
+#include <linux/types.h>
+
+extern int ic_proto_enabled;	/* Protocols enabled (see IC_xxx) */
+extern int ic_set_manually;	/* IPconfig parameters set manually */
+
+extern __be32 ic_myaddr;		/* My IP address */
+extern __be32 ic_gateway;		/* Gateway IP address */
+
+extern __be32 ic_servaddr;		/* Boot server IP address */
+
+extern __be32 root_server_addr;	/* Address of NFS server */
+extern u8 root_server_path[];	/* Path to mount as root */
+
+
+/* bits in ic_proto_{enabled,used} */
+#define IC_PROTO	0xFF	/* Protocols mask: */
+#define IC_BOOTP	0x01	/*   BOOTP (or DHCP, see below) */
+#define IC_RARP		0x02	/*   RARP */
+#define IC_USE_DHCP    0x100	/* If on, use DHCP instead of BOOTP */