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, 145 insertions, 0 deletions

diff --git a/drivers/misc/smpro-misc.c b/drivers/misc/smpro-misc.c
new file mode 100644
index 000000000..6c427141e
--- /dev/null
+++ b/drivers/misc/smpro-misc.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Ampere Computing SoC's SMpro Misc Driver
+ *
+ * Copyright (c) 2022, Ampere Computing LLC
+ */
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+/* Boot Stage/Progress Registers */
+#define BOOTSTAGE	0xB0
+#define BOOTSTAGE_LO	0xB1
+#define CUR_BOOTSTAGE	0xB2
+#define BOOTSTAGE_HI	0xB3
+
+/* SOC State Registers */
+#define SOC_POWER_LIMIT		0xE5
+
+struct smpro_misc {
+	struct regmap *regmap;
+};
+
+static ssize_t boot_progress_show(struct device *dev, struct device_attribute *da, char *buf)
+{
+	struct smpro_misc *misc = dev_get_drvdata(dev);
+	u16 boot_progress[3] = { 0 };
+	u32 bootstage;
+	u8 boot_stage;
+	u8 cur_stage;
+	u32 reg_lo;
+	u32 reg;
+	int ret;
+
+	/* Read current boot stage */
+	ret = regmap_read(misc->regmap, CUR_BOOTSTAGE, &reg);
+	if (ret)
+		return ret;
+
+	cur_stage = reg & 0xff;
+
+	ret = regmap_read(misc->regmap, BOOTSTAGE, &bootstage);
+	if (ret)
+		return ret;
+
+	boot_stage = (bootstage >> 8) & 0xff;
+
+	if (boot_stage > cur_stage)
+		return -EINVAL;
+
+	ret = regmap_read(misc->regmap,	BOOTSTAGE_LO, &reg_lo);
+	if (!ret)
+		ret = regmap_read(misc->regmap, BOOTSTAGE_HI, &reg);
+	if (ret)
+		return ret;
+
+	/* Firmware to report new boot stage next time */
+	if (boot_stage < cur_stage) {
+		ret = regmap_write(misc->regmap, BOOTSTAGE, ((bootstage & 0xff00) | 0x1));
+		if (ret)
+			return ret;
+	}
+
+	boot_progress[0] = bootstage;
+	boot_progress[1] = swab16(reg);
+	boot_progress[2] = swab16(reg_lo);
+
+	return sysfs_emit(buf, "%*phN\n", (int)sizeof(boot_progress), boot_progress);
+}
+
+static DEVICE_ATTR_RO(boot_progress);
+
+static ssize_t soc_power_limit_show(struct device *dev, struct device_attribute *da, char *buf)
+{
+	struct smpro_misc *misc = dev_get_drvdata(dev);
+	unsigned int value;
+	int ret;
+
+	ret = regmap_read(misc->regmap, SOC_POWER_LIMIT, &value);
+	if (ret)
+		return ret;
+
+	return sysfs_emit(buf, "%d\n", value);
+}
+
+static ssize_t soc_power_limit_store(struct device *dev, struct device_attribute *da,
+				     const char *buf, size_t count)
+{
+	struct smpro_misc *misc = dev_get_drvdata(dev);
+	unsigned long val;
+	s32 ret;
+
+	ret = kstrtoul(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	ret = regmap_write(misc->regmap, SOC_POWER_LIMIT, (unsigned int)val);
+	if (ret)
+		return -EPROTO;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(soc_power_limit);
+
+static struct attribute *smpro_misc_attrs[] = {
+	&dev_attr_boot_progress.attr,
+	&dev_attr_soc_power_limit.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(smpro_misc);
+
+static int smpro_misc_probe(struct platform_device *pdev)
+{
+	struct smpro_misc *misc;
+
+	misc = devm_kzalloc(&pdev->dev, sizeof(struct smpro_misc), GFP_KERNEL);
+	if (!misc)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, misc);
+
+	misc->regmap = dev_get_regmap(pdev->dev.parent, NULL);
+	if (!misc->regmap)
+		return -ENODEV;
+
+	return 0;
+}
+
+static struct platform_driver smpro_misc_driver = {
+	.probe		= smpro_misc_probe,
+	.driver = {
+		.name	= "smpro-misc",
+		.dev_groups = smpro_misc_groups,
+	},
+};
+
+module_platform_driver(smpro_misc_driver);
+
+MODULE_AUTHOR("Tung Nguyen <tungnguyen@os.amperecomputing.com>");
+MODULE_AUTHOR("Quan Nguyen <quan@os.amperecomputing.com>");
+MODULE_DESCRIPTION("Ampere Altra SMpro Misc driver");
+MODULE_LICENSE("GPL");