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, 92 insertions, 0 deletions

diff --git a/drivers/rtc/proc.c b/drivers/rtc/proc.c
new file mode 100644
index 000000000..cbcdbb19d
--- /dev/null
+++ b/drivers/rtc/proc.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * RTC subsystem, proc interface
+ *
+ * Copyright (C) 2005-06 Tower Technologies
+ * Author: Alessandro Zummo <a.zummo@towertech.it>
+ *
+ * based on arch/arm/common/rtctime.c
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+
+#include "rtc-core.h"
+
+#define NAME_SIZE	10
+
+#if defined(CONFIG_RTC_HCTOSYS_DEVICE)
+static bool is_rtc_hctosys(struct rtc_device *rtc)
+{
+	int size;
+	char name[NAME_SIZE];
+
+	size = snprintf(name, NAME_SIZE, "rtc%d", rtc->id);
+	if (size >= NAME_SIZE)
+		return false;
+
+	return !strncmp(name, CONFIG_RTC_HCTOSYS_DEVICE, NAME_SIZE);
+}
+#else
+static bool is_rtc_hctosys(struct rtc_device *rtc)
+{
+	return (rtc->id == 0);
+}
+#endif
+
+static int rtc_proc_show(struct seq_file *seq, void *offset)
+{
+	int err;
+	struct rtc_device *rtc = seq->private;
+	const struct rtc_class_ops *ops = rtc->ops;
+	struct rtc_wkalrm alrm;
+	struct rtc_time tm;
+
+	err = rtc_read_time(rtc, &tm);
+	if (err == 0) {
+		seq_printf(seq,
+			   "rtc_time\t: %ptRt\n"
+			   "rtc_date\t: %ptRd\n",
+			   &tm, &tm);
+	}
+
+	err = rtc_read_alarm(rtc, &alrm);
+	if (err == 0) {
+		seq_printf(seq, "alrm_time\t: %ptRt\n", &alrm.time);
+		seq_printf(seq, "alrm_date\t: %ptRd\n", &alrm.time);
+		seq_printf(seq, "alarm_IRQ\t: %s\n",
+			   alrm.enabled ? "yes" : "no");
+		seq_printf(seq, "alrm_pending\t: %s\n",
+			   alrm.pending ? "yes" : "no");
+		seq_printf(seq, "update IRQ enabled\t: %s\n",
+			   (rtc->uie_rtctimer.enabled) ? "yes" : "no");
+		seq_printf(seq, "periodic IRQ enabled\t: %s\n",
+			   (rtc->pie_enabled) ? "yes" : "no");
+		seq_printf(seq, "periodic IRQ frequency\t: %d\n",
+			   rtc->irq_freq);
+		seq_printf(seq, "max user IRQ frequency\t: %d\n",
+			   rtc->max_user_freq);
+	}
+
+	seq_printf(seq, "24hr\t\t: yes\n");
+
+	if (ops->proc)
+		ops->proc(rtc->dev.parent, seq);
+
+	return 0;
+}
+
+void rtc_proc_add_device(struct rtc_device *rtc)
+{
+	if (is_rtc_hctosys(rtc))
+		proc_create_single_data("driver/rtc", 0, NULL, rtc_proc_show,
+					rtc);
+}
+
+void rtc_proc_del_device(struct rtc_device *rtc)
+{
+	if (is_rtc_hctosys(rtc))
+		remove_proc_entry("driver/rtc", NULL);
+}