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, 249 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-msc313.c b/drivers/rtc/rtc-msc313.c
new file mode 100644
index 000000000..6ef9c4efd
--- /dev/null
+++ b/drivers/rtc/rtc-msc313.c
@@ -0,0 +1,249 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Real time clocks driver for MStar/SigmaStar ARMv7 SoCs.
+ * Based on "Real Time Clock driver for msb252x." that was contained
+ * in various MStar kernels.
+ *
+ * (C) 2019 Daniel Palmer
+ * (C) 2021 Romain Perier
+ */
+
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+/* Registers */
+#define REG_RTC_CTRL		0x00
+#define REG_RTC_FREQ_CW_L	0x04
+#define REG_RTC_FREQ_CW_H	0x08
+#define REG_RTC_LOAD_VAL_L	0x0C
+#define REG_RTC_LOAD_VAL_H	0x10
+#define REG_RTC_MATCH_VAL_L	0x14
+#define REG_RTC_MATCH_VAL_H	0x18
+#define REG_RTC_STATUS_INT	0x1C
+#define REG_RTC_CNT_VAL_L	0x20
+#define REG_RTC_CNT_VAL_H	0x24
+
+/* Control bits for REG_RTC_CTRL */
+#define SOFT_RSTZ_BIT		BIT(0)
+#define CNT_EN_BIT		BIT(1)
+#define WRAP_EN_BIT		BIT(2)
+#define LOAD_EN_BIT		BIT(3)
+#define READ_EN_BIT		BIT(4)
+#define INT_MASK_BIT		BIT(5)
+#define INT_FORCE_BIT		BIT(6)
+#define INT_CLEAR_BIT		BIT(7)
+
+/* Control bits for REG_RTC_STATUS_INT */
+#define RAW_INT_BIT		BIT(0)
+#define ALM_INT_BIT		BIT(1)
+
+struct msc313_rtc {
+	struct rtc_device *rtc_dev;
+	void __iomem *rtc_base;
+};
+
+static int msc313_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct msc313_rtc *priv = dev_get_drvdata(dev);
+	unsigned long seconds;
+
+	seconds = readw(priv->rtc_base + REG_RTC_MATCH_VAL_L)
+			| ((unsigned long)readw(priv->rtc_base + REG_RTC_MATCH_VAL_H) << 16);
+
+	rtc_time64_to_tm(seconds, &alarm->time);
+
+	if (!(readw(priv->rtc_base + REG_RTC_CTRL) & INT_MASK_BIT))
+		alarm->enabled = 1;
+
+	return 0;
+}
+
+static int msc313_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct msc313_rtc *priv = dev_get_drvdata(dev);
+	u16 reg;
+
+	reg = readw(priv->rtc_base + REG_RTC_CTRL);
+	if (enabled)
+		reg &= ~INT_MASK_BIT;
+	else
+		reg |= INT_MASK_BIT;
+	writew(reg, priv->rtc_base + REG_RTC_CTRL);
+	return 0;
+}
+
+static int msc313_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct msc313_rtc *priv = dev_get_drvdata(dev);
+	unsigned long seconds;
+
+	seconds = rtc_tm_to_time64(&alarm->time);
+	writew((seconds & 0xFFFF), priv->rtc_base + REG_RTC_MATCH_VAL_L);
+	writew((seconds >> 16) & 0xFFFF, priv->rtc_base + REG_RTC_MATCH_VAL_H);
+
+	msc313_rtc_alarm_irq_enable(dev, alarm->enabled);
+
+	return 0;
+}
+
+static bool msc313_rtc_get_enabled(struct msc313_rtc *priv)
+{
+	return readw(priv->rtc_base + REG_RTC_CTRL) & CNT_EN_BIT;
+}
+
+static void msc313_rtc_set_enabled(struct msc313_rtc *priv)
+{
+	u16 reg;
+
+	reg = readw(priv->rtc_base + REG_RTC_CTRL);
+	reg |= CNT_EN_BIT;
+	writew(reg, priv->rtc_base + REG_RTC_CTRL);
+}
+
+static int msc313_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct msc313_rtc *priv = dev_get_drvdata(dev);
+	u32 seconds;
+	u16 reg;
+
+	if (!msc313_rtc_get_enabled(priv))
+		return -EINVAL;
+
+	reg = readw(priv->rtc_base + REG_RTC_CTRL);
+	writew(reg | READ_EN_BIT, priv->rtc_base + REG_RTC_CTRL);
+
+	/* Wait for HW latch done */
+	while (readw(priv->rtc_base + REG_RTC_CTRL) & READ_EN_BIT)
+		udelay(1);
+
+	seconds = readw(priv->rtc_base + REG_RTC_CNT_VAL_L)
+			| ((unsigned long)readw(priv->rtc_base + REG_RTC_CNT_VAL_H) << 16);
+
+	rtc_time64_to_tm(seconds, tm);
+
+	return 0;
+}
+
+static int msc313_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct msc313_rtc *priv = dev_get_drvdata(dev);
+	unsigned long seconds;
+	u16 reg;
+
+	seconds = rtc_tm_to_time64(tm);
+	writew(seconds & 0xFFFF, priv->rtc_base + REG_RTC_LOAD_VAL_L);
+	writew((seconds >> 16) & 0xFFFF, priv->rtc_base + REG_RTC_LOAD_VAL_H);
+
+	/* Enable load for loading value into internal RTC counter */
+	reg = readw(priv->rtc_base + REG_RTC_CTRL);
+	writew(reg | LOAD_EN_BIT, priv->rtc_base + REG_RTC_CTRL);
+
+	/* Wait for HW latch done */
+	while (readw(priv->rtc_base + REG_RTC_CTRL) & LOAD_EN_BIT)
+		udelay(1);
+	msc313_rtc_set_enabled(priv);
+	return 0;
+}
+
+static const struct rtc_class_ops msc313_rtc_ops = {
+	.read_time = msc313_rtc_read_time,
+	.set_time = msc313_rtc_set_time,
+	.read_alarm = msc313_rtc_read_alarm,
+	.set_alarm = msc313_rtc_set_alarm,
+	.alarm_irq_enable = msc313_rtc_alarm_irq_enable,
+};
+
+static irqreturn_t msc313_rtc_interrupt(s32 irq, void *dev_id)
+{
+	struct msc313_rtc *priv = dev_id;
+	u16 reg;
+
+	reg = readw(priv->rtc_base + REG_RTC_STATUS_INT);
+	if (!(reg & ALM_INT_BIT))
+		return IRQ_NONE;
+
+	reg = readw(priv->rtc_base + REG_RTC_CTRL);
+	reg |= INT_CLEAR_BIT;
+	reg &= ~INT_FORCE_BIT;
+	writew(reg, priv->rtc_base + REG_RTC_CTRL);
+
+	rtc_update_irq(priv->rtc_dev, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static int msc313_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct msc313_rtc *priv;
+	unsigned long rate;
+	struct clk *clk;
+	int ret;
+	int irq;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(struct msc313_rtc), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->rtc_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->rtc_base))
+		return PTR_ERR(priv->rtc_base);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return -EINVAL;
+
+	priv->rtc_dev = devm_rtc_allocate_device(dev);
+	if (IS_ERR(priv->rtc_dev))
+		return PTR_ERR(priv->rtc_dev);
+
+	priv->rtc_dev->ops = &msc313_rtc_ops;
+	priv->rtc_dev->range_max = U32_MAX;
+
+	ret = devm_request_irq(dev, irq, msc313_rtc_interrupt, IRQF_SHARED,
+			       dev_name(&pdev->dev), priv);
+	if (ret) {
+		dev_err(dev, "Could not request IRQ\n");
+		return ret;
+	}
+
+	clk = devm_clk_get_enabled(dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(dev, "No input reference clock\n");
+		return PTR_ERR(clk);
+	}
+
+	rate = clk_get_rate(clk);
+	writew(rate & 0xFFFF, priv->rtc_base + REG_RTC_FREQ_CW_L);
+	writew((rate >> 16) & 0xFFFF, priv->rtc_base + REG_RTC_FREQ_CW_H);
+
+	platform_set_drvdata(pdev, priv);
+
+	return devm_rtc_register_device(priv->rtc_dev);
+}
+
+static const struct of_device_id msc313_rtc_of_match_table[] = {
+	{ .compatible = "mstar,msc313-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, msc313_rtc_of_match_table);
+
+static struct platform_driver msc313_rtc_driver = {
+	.probe = msc313_rtc_probe,
+	.driver = {
+		.name = "msc313-rtc",
+		.of_match_table = msc313_rtc_of_match_table,
+	},
+};
+
+module_platform_driver(msc313_rtc_driver);
+
+MODULE_AUTHOR("Daniel Palmer <daniel@thingy.jp>");
+MODULE_AUTHOR("Romain Perier <romain.perier@gmail.com>");
+MODULE_DESCRIPTION("MStar RTC Driver");
+MODULE_LICENSE("GPL v2");