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, 109 insertions, 0 deletions

diff --git a/net/rds/sysctl.c b/net/rds/sysctl.c
new file mode 100644
index 000000000..025f518a4
--- /dev/null
+++ b/net/rds/sysctl.c
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2006 Oracle.  All rights reserved.
+ *
+ * This software is available to you under a choice of one of two
+ * licenses.  You may choose to be licensed under the terms of the GNU
+ * General Public License (GPL) Version 2, available from the file
+ * COPYING in the main directory of this source tree, or the
+ * OpenIB.org BSD license below:
+ *
+ *     Redistribution and use in source and binary forms, with or
+ *     without modification, are permitted provided that the following
+ *     conditions are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the following
+ *        disclaimer in the documentation and/or other materials
+ *        provided with the distribution.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+#include <linux/kernel.h>
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+
+#include "rds.h"
+
+static struct ctl_table_header *rds_sysctl_reg_table;
+
+static unsigned long rds_sysctl_reconnect_min = 1;
+static unsigned long rds_sysctl_reconnect_max = ~0UL;
+
+unsigned long rds_sysctl_reconnect_min_jiffies;
+unsigned long rds_sysctl_reconnect_max_jiffies = HZ;
+
+unsigned int  rds_sysctl_max_unacked_packets = 8;
+unsigned int  rds_sysctl_max_unacked_bytes = (16 << 20);
+
+unsigned int rds_sysctl_ping_enable = 1;
+
+static struct ctl_table rds_sysctl_rds_table[] = {
+	{
+		.procname       = "reconnect_min_delay_ms",
+		.data		= &rds_sysctl_reconnect_min_jiffies,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_ms_jiffies_minmax,
+		.extra1		= &rds_sysctl_reconnect_min,
+		.extra2		= &rds_sysctl_reconnect_max_jiffies,
+	},
+	{
+		.procname       = "reconnect_max_delay_ms",
+		.data		= &rds_sysctl_reconnect_max_jiffies,
+		.maxlen         = sizeof(unsigned long),
+		.mode           = 0644,
+		.proc_handler   = proc_doulongvec_ms_jiffies_minmax,
+		.extra1		= &rds_sysctl_reconnect_min_jiffies,
+		.extra2		= &rds_sysctl_reconnect_max,
+	},
+	{
+		.procname	= "max_unacked_packets",
+		.data		= &rds_sysctl_max_unacked_packets,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
+		.procname	= "max_unacked_bytes",
+		.data		= &rds_sysctl_max_unacked_bytes,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
+		.procname	= "ping_enable",
+		.data		= &rds_sysctl_ping_enable,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+};
+
+void rds_sysctl_exit(void)
+{
+	unregister_net_sysctl_table(rds_sysctl_reg_table);
+}
+
+int rds_sysctl_init(void)
+{
+	rds_sysctl_reconnect_min = msecs_to_jiffies(1);
+	rds_sysctl_reconnect_min_jiffies = rds_sysctl_reconnect_min;
+
+	rds_sysctl_reg_table =
+		register_net_sysctl(&init_net, "net/rds", rds_sysctl_rds_table);
+	if (!rds_sysctl_reg_table)
+		return -ENOMEM;
+	return 0;
+}