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>

3 files changed, 131 insertions, 0 deletions

diff --git a/samples/pfsm/.gitignore b/samples/pfsm/.gitignore
new file mode 100644
index 000000000..f350a030a
--- /dev/null
+++ b/samples/pfsm/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0
+/pfsm-wakeup
diff --git a/samples/pfsm/Makefile b/samples/pfsm/Makefile
new file mode 100644
index 000000000..213e8d9f5
--- /dev/null
+++ b/samples/pfsm/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+userprogs-always-y += pfsm-wakeup
+
+userccflags += -I usr/include
diff --git a/samples/pfsm/pfsm-wakeup.c b/samples/pfsm/pfsm-wakeup.c
new file mode 100644
index 000000000..299dd9e1f
--- /dev/null
+++ b/samples/pfsm/pfsm-wakeup.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * TPS6594 PFSM userspace example
+ *
+ * Copyright (C) 2023 BayLibre Incorporated - https://www.baylibre.com/
+ *
+ * This example shows how to use PFSMs from a userspace application,
+ * on TI j721s2 platform. The PMIC is armed to be triggered by a RTC
+ * alarm to execute state transition (RETENTION to ACTIVE).
+ */
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include <linux/rtc.h>
+#include <linux/tps6594_pfsm.h>
+
+#define ALARM_DELTA_SEC 30
+
+#define RTC_A "/dev/rtc0"
+
+#define PMIC_NB 3
+#define PMIC_A "/dev/pfsm-0-0x48"
+#define PMIC_B "/dev/pfsm-0-0x4c"
+#define PMIC_C "/dev/pfsm-2-0x58"
+
+static const char * const dev_pfsm[] = {PMIC_A, PMIC_B, PMIC_C};
+
+int main(int argc, char *argv[])
+{
+	int i, ret, fd_rtc, fd_pfsm[PMIC_NB] = { 0 };
+	struct rtc_time rtc_tm;
+	struct pmic_state_opt pmic_opt = { 0 };
+	unsigned long data;
+
+	fd_rtc = open(RTC_A, O_RDONLY);
+	if (fd_rtc < 0) {
+		perror("Failed to open RTC device.");
+		goto out;
+	}
+
+	for (i = 0 ; i < PMIC_NB ; i++) {
+		fd_pfsm[i] = open(dev_pfsm[i], O_RDWR);
+		if (fd_pfsm[i] < 0) {
+			perror("Failed to open PFSM device.");
+			goto out;
+		}
+	}
+
+	/* Read RTC date/time */
+	ret = ioctl(fd_rtc, RTC_RD_TIME, &rtc_tm);
+	if (ret < 0) {
+		perror("Failed to read RTC date/time.");
+		goto out;
+	}
+	printf("Current RTC date/time is %d-%d-%d, %02d:%02d:%02d.\n",
+	       rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900,
+	       rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);
+
+	/* Set RTC alarm to ALARM_DELTA_SEC sec in the future, and check for rollover */
+	rtc_tm.tm_sec += ALARM_DELTA_SEC;
+	if (rtc_tm.tm_sec >= 60) {
+		rtc_tm.tm_sec %= 60;
+		rtc_tm.tm_min++;
+	}
+	if (rtc_tm.tm_min == 60) {
+		rtc_tm.tm_min = 0;
+		rtc_tm.tm_hour++;
+	}
+	if (rtc_tm.tm_hour == 24)
+		rtc_tm.tm_hour = 0;
+	ret = ioctl(fd_rtc, RTC_ALM_SET, &rtc_tm);
+	if (ret < 0) {
+		perror("Failed to set RTC alarm.");
+		goto out;
+	}
+
+	/* Enable alarm interrupts */
+	ret = ioctl(fd_rtc, RTC_AIE_ON, 0);
+	if (ret < 0) {
+		perror("Failed to enable alarm interrupts.");
+		goto out;
+	}
+	printf("Waiting %d seconds for alarm...\n", ALARM_DELTA_SEC);
+
+	/*
+	 * Set RETENTION state with options for PMIC_C/B/A respectively.
+	 * Since PMIC_A is master, it should be the last one to be configured.
+	 */
+	pmic_opt.ddr_retention = 1;
+	for (i = PMIC_NB - 1 ; i >= 0 ; i--) {
+		printf("Set RETENTION state for PMIC_%d.\n", i);
+		sleep(1);
+		ret = ioctl(fd_pfsm[i], PMIC_SET_RETENTION_STATE, &pmic_opt);
+		if (ret < 0) {
+			perror("Failed to set RETENTION state.");
+			goto out_reset;
+		}
+	}
+
+	/* This blocks until the alarm ring causes an interrupt */
+	ret = read(fd_rtc, &data, sizeof(unsigned long));
+	if (ret < 0)
+		perror("Failed to get RTC alarm.");
+	else
+		puts("Alarm rang.\n");
+
+out_reset:
+	ioctl(fd_rtc, RTC_AIE_OFF, 0);
+
+	/* Set ACTIVE state for PMIC_A */
+	ioctl(fd_pfsm[0], PMIC_SET_ACTIVE_STATE, 0);
+
+out:
+	for (i = 0 ; i < PMIC_NB ; i++)
+		if (fd_pfsm[i])
+			close(fd_pfsm[i]);
+
+	if (fd_rtc)
+		close(fd_rtc);
+
+	return 0;
+}