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, 45 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-probe.c b/drivers/clocksource/timer-probe.c
new file mode 100644
index 000000000..b7860bc0d
--- /dev/null
+++ b/drivers/clocksource/timer-probe.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2012, NVIDIA CORPORATION.  All rights reserved.
+ */
+
+#include <linux/acpi.h>
+#include <linux/init.h>
+#include <linux/of.h>
+#include <linux/clocksource.h>
+
+extern struct of_device_id __timer_of_table[];
+
+static const struct of_device_id __timer_of_table_sentinel
+	__used __section("__timer_of_table_end");
+
+void __init timer_probe(void)
+{
+	struct device_node *np;
+	const struct of_device_id *match;
+	of_init_fn_1_ret init_func_ret;
+	unsigned timers = 0;
+	int ret;
+
+	for_each_matching_node_and_match(np, __timer_of_table, &match) {
+		if (!of_device_is_available(np))
+			continue;
+
+		init_func_ret = match->data;
+
+		ret = init_func_ret(np);
+		if (ret) {
+			if (ret != -EPROBE_DEFER)
+				pr_err("Failed to initialize '%pOF': %d\n", np,
+				       ret);
+			continue;
+		}
+
+		timers++;
+	}
+
+	timers += acpi_probe_device_table(timer);
+
+	if (!timers)
+		pr_crit("%s: no matching timers found\n", __func__);
+}