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, 130 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-aspeed.c b/drivers/rtc/rtc-aspeed.c
new file mode 100644
index 000000000..8f5b440f8
--- /dev/null
+++ b/drivers/rtc/rtc-aspeed.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0+
+// Copyright 2015 IBM Corp.
+
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/io.h>
+
+struct aspeed_rtc {
+	void __iomem *base;
+};
+
+#define RTC_TIME	0x00
+#define RTC_YEAR	0x04
+#define RTC_CTRL	0x10
+
+#define RTC_UNLOCK	BIT(1)
+#define RTC_ENABLE	BIT(0)
+
+static int aspeed_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct aspeed_rtc *rtc = dev_get_drvdata(dev);
+	unsigned int cent, year;
+	u32 reg1, reg2;
+
+	if (!(readl(rtc->base + RTC_CTRL) & RTC_ENABLE)) {
+		dev_dbg(dev, "%s failing as rtc disabled\n", __func__);
+		return -EINVAL;
+	}
+
+	do {
+		reg2 = readl(rtc->base + RTC_YEAR);
+		reg1 = readl(rtc->base + RTC_TIME);
+	} while (reg2 != readl(rtc->base + RTC_YEAR));
+
+	tm->tm_mday = (reg1 >> 24) & 0x1f;
+	tm->tm_hour = (reg1 >> 16) & 0x1f;
+	tm->tm_min = (reg1 >> 8) & 0x3f;
+	tm->tm_sec = (reg1 >> 0) & 0x3f;
+
+	cent = (reg2 >> 16) & 0x1f;
+	year = (reg2 >> 8) & 0x7f;
+	tm->tm_mon = ((reg2 >>  0) & 0x0f) - 1;
+	tm->tm_year = year + (cent * 100) - 1900;
+
+	dev_dbg(dev, "%s %ptR", __func__, tm);
+
+	return 0;
+}
+
+static int aspeed_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct aspeed_rtc *rtc = dev_get_drvdata(dev);
+	u32 reg1, reg2, ctrl;
+	int year, cent;
+
+	cent = (tm->tm_year + 1900) / 100;
+	year = tm->tm_year % 100;
+
+	reg1 = (tm->tm_mday << 24) | (tm->tm_hour << 16) | (tm->tm_min << 8) |
+		tm->tm_sec;
+
+	reg2 = ((cent & 0x1f) << 16) | ((year & 0x7f) << 8) |
+		((tm->tm_mon + 1) & 0xf);
+
+	ctrl = readl(rtc->base + RTC_CTRL);
+	writel(ctrl | RTC_UNLOCK, rtc->base + RTC_CTRL);
+
+	writel(reg1, rtc->base + RTC_TIME);
+	writel(reg2, rtc->base + RTC_YEAR);
+
+	/* Re-lock and ensure enable is set now that a time is programmed */
+	writel(ctrl | RTC_ENABLE, rtc->base + RTC_CTRL);
+
+	return 0;
+}
+
+static const struct rtc_class_ops aspeed_rtc_ops = {
+	.read_time = aspeed_rtc_read_time,
+	.set_time = aspeed_rtc_set_time,
+};
+
+static int aspeed_rtc_probe(struct platform_device *pdev)
+{
+	struct aspeed_rtc *rtc;
+	struct rtc_device *rtc_dev;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(rtc->base))
+		return PTR_ERR(rtc->base);
+
+	rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc_dev))
+		return PTR_ERR(rtc_dev);
+
+	platform_set_drvdata(pdev, rtc);
+
+	rtc_dev->ops = &aspeed_rtc_ops;
+	rtc_dev->range_min = RTC_TIMESTAMP_BEGIN_1900;
+	rtc_dev->range_max = 38814989399LL; /* 3199-12-31 23:59:59 */
+
+	return devm_rtc_register_device(rtc_dev);
+}
+
+static const struct of_device_id aspeed_rtc_match[] = {
+	{ .compatible = "aspeed,ast2400-rtc", },
+	{ .compatible = "aspeed,ast2500-rtc", },
+	{ .compatible = "aspeed,ast2600-rtc", },
+	{ .compatible = "aspeed,ast2700-rtc", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, aspeed_rtc_match);
+
+static struct platform_driver aspeed_rtc_driver = {
+	.driver = {
+		.name = "aspeed-rtc",
+		.of_match_table = aspeed_rtc_match,
+	},
+};
+
+module_platform_driver_probe(aspeed_rtc_driver, aspeed_rtc_probe);
+
+MODULE_DESCRIPTION("ASPEED RTC driver");
+MODULE_AUTHOR("Joel Stanley <joel@jms.id.au>");
+MODULE_LICENSE("GPL");