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, 206 insertions, 0 deletions

diff --git a/arch/mips/bcm63xx/timer.c b/arch/mips/bcm63xx/timer.c
new file mode 100644
index 000000000..74b83807d
--- /dev/null
+++ b/arch/mips/bcm63xx/timer.c
@@ -0,0 +1,206 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2008 Maxime Bizon <mbizon@freebox.fr>
+ */
+
+#include <linux/kernel.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/export.h>
+#include <linux/spinlock.h>
+#include <linux/interrupt.h>
+#include <linux/clk.h>
+#include <bcm63xx_cpu.h>
+#include <bcm63xx_io.h>
+#include <bcm63xx_timer.h>
+#include <bcm63xx_regs.h>
+
+static DEFINE_RAW_SPINLOCK(timer_reg_lock);
+static DEFINE_RAW_SPINLOCK(timer_data_lock);
+static struct clk *periph_clk;
+
+static struct timer_data {
+	void	(*cb)(void *);
+	void	*data;
+} timer_data[BCM63XX_TIMER_COUNT];
+
+static irqreturn_t timer_interrupt(int irq, void *dev_id)
+{
+	u32 stat;
+	int i;
+
+	raw_spin_lock(&timer_reg_lock);
+	stat = bcm_timer_readl(TIMER_IRQSTAT_REG);
+	bcm_timer_writel(stat, TIMER_IRQSTAT_REG);
+	raw_spin_unlock(&timer_reg_lock);
+
+	for (i = 0; i < BCM63XX_TIMER_COUNT; i++) {
+		if (!(stat & TIMER_IRQSTAT_TIMER_CAUSE(i)))
+			continue;
+
+		raw_spin_lock(&timer_data_lock);
+		if (!timer_data[i].cb) {
+			raw_spin_unlock(&timer_data_lock);
+			continue;
+		}
+
+		timer_data[i].cb(timer_data[i].data);
+		raw_spin_unlock(&timer_data_lock);
+	}
+
+	return IRQ_HANDLED;
+}
+
+int bcm63xx_timer_enable(int id)
+{
+	u32 reg;
+	unsigned long flags;
+
+	if (id >= BCM63XX_TIMER_COUNT)
+		return -EINVAL;
+
+	raw_spin_lock_irqsave(&timer_reg_lock, flags);
+
+	reg = bcm_timer_readl(TIMER_CTLx_REG(id));
+	reg |= TIMER_CTL_ENABLE_MASK;
+	bcm_timer_writel(reg, TIMER_CTLx_REG(id));
+
+	reg = bcm_timer_readl(TIMER_IRQSTAT_REG);
+	reg |= TIMER_IRQSTAT_TIMER_IR_EN(id);
+	bcm_timer_writel(reg, TIMER_IRQSTAT_REG);
+
+	raw_spin_unlock_irqrestore(&timer_reg_lock, flags);
+	return 0;
+}
+
+EXPORT_SYMBOL(bcm63xx_timer_enable);
+
+int bcm63xx_timer_disable(int id)
+{
+	u32 reg;
+	unsigned long flags;
+
+	if (id >= BCM63XX_TIMER_COUNT)
+		return -EINVAL;
+
+	raw_spin_lock_irqsave(&timer_reg_lock, flags);
+
+	reg = bcm_timer_readl(TIMER_CTLx_REG(id));
+	reg &= ~TIMER_CTL_ENABLE_MASK;
+	bcm_timer_writel(reg, TIMER_CTLx_REG(id));
+
+	reg = bcm_timer_readl(TIMER_IRQSTAT_REG);
+	reg &= ~TIMER_IRQSTAT_TIMER_IR_EN(id);
+	bcm_timer_writel(reg, TIMER_IRQSTAT_REG);
+
+	raw_spin_unlock_irqrestore(&timer_reg_lock, flags);
+	return 0;
+}
+
+EXPORT_SYMBOL(bcm63xx_timer_disable);
+
+int bcm63xx_timer_register(int id, void (*callback)(void *data), void *data)
+{
+	unsigned long flags;
+	int ret;
+
+	if (id >= BCM63XX_TIMER_COUNT || !callback)
+		return -EINVAL;
+
+	ret = 0;
+	raw_spin_lock_irqsave(&timer_data_lock, flags);
+	if (timer_data[id].cb) {
+		ret = -EBUSY;
+		goto out;
+	}
+
+	timer_data[id].cb = callback;
+	timer_data[id].data = data;
+
+out:
+	raw_spin_unlock_irqrestore(&timer_data_lock, flags);
+	return ret;
+}
+
+EXPORT_SYMBOL(bcm63xx_timer_register);
+
+void bcm63xx_timer_unregister(int id)
+{
+	unsigned long flags;
+
+	if (id >= BCM63XX_TIMER_COUNT)
+		return;
+
+	raw_spin_lock_irqsave(&timer_data_lock, flags);
+	timer_data[id].cb = NULL;
+	raw_spin_unlock_irqrestore(&timer_data_lock, flags);
+}
+
+EXPORT_SYMBOL(bcm63xx_timer_unregister);
+
+unsigned int bcm63xx_timer_countdown(unsigned int countdown_us)
+{
+	return (clk_get_rate(periph_clk) / (1000 * 1000)) * countdown_us;
+}
+
+EXPORT_SYMBOL(bcm63xx_timer_countdown);
+
+int bcm63xx_timer_set(int id, int monotonic, unsigned int countdown_us)
+{
+	u32 reg, countdown;
+	unsigned long flags;
+
+	if (id >= BCM63XX_TIMER_COUNT)
+		return -EINVAL;
+
+	countdown = bcm63xx_timer_countdown(countdown_us);
+	if (countdown & ~TIMER_CTL_COUNTDOWN_MASK)
+		return -EINVAL;
+
+	raw_spin_lock_irqsave(&timer_reg_lock, flags);
+	reg = bcm_timer_readl(TIMER_CTLx_REG(id));
+
+	if (monotonic)
+		reg &= ~TIMER_CTL_MONOTONIC_MASK;
+	else
+		reg |= TIMER_CTL_MONOTONIC_MASK;
+
+	reg &= ~TIMER_CTL_COUNTDOWN_MASK;
+	reg |= countdown;
+	bcm_timer_writel(reg, TIMER_CTLx_REG(id));
+
+	raw_spin_unlock_irqrestore(&timer_reg_lock, flags);
+	return 0;
+}
+
+EXPORT_SYMBOL(bcm63xx_timer_set);
+
+static int bcm63xx_timer_init(void)
+{
+	int ret, irq;
+	u32 reg;
+
+	reg = bcm_timer_readl(TIMER_IRQSTAT_REG);
+	reg &= ~TIMER_IRQSTAT_TIMER0_IR_EN;
+	reg &= ~TIMER_IRQSTAT_TIMER1_IR_EN;
+	reg &= ~TIMER_IRQSTAT_TIMER2_IR_EN;
+	bcm_timer_writel(reg, TIMER_IRQSTAT_REG);
+
+	periph_clk = clk_get(NULL, "periph");
+	if (IS_ERR(periph_clk))
+		return -ENODEV;
+
+	irq = bcm63xx_get_irq_number(IRQ_TIMER);
+	ret = request_irq(irq, timer_interrupt, 0, "bcm63xx_timer", NULL);
+	if (ret) {
+		pr_err("%s: failed to register irq\n", __func__);
+		return ret;
+	}
+
+	return 0;
+}
+
+arch_initcall(bcm63xx_timer_init);