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, 253 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-msc313e.c b/drivers/clocksource/timer-msc313e.c
new file mode 100644
index 000000000..e4b9e3f16
--- /dev/null
+++ b/drivers/clocksource/timer-msc313e.c
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * MStar timer driver
+ *
+ * Copyright (C) 2021 Daniel Palmer
+ * Copyright (C) 2021 Romain Perier
+ *
+ */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/irqreturn.h>
+#include <linux/sched_clock.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+
+#ifdef CONFIG_ARM
+#include <linux/delay.h>
+#endif
+
+#include "timer-of.h"
+
+#define TIMER_NAME "msc313e_timer"
+
+#define MSC313E_REG_CTRL		0x00
+#define MSC313E_REG_CTRL_TIMER_EN	BIT(0)
+#define MSC313E_REG_CTRL_TIMER_TRIG	BIT(1)
+#define MSC313E_REG_CTRL_TIMER_INT_EN	BIT(8)
+#define MSC313E_REG_TIMER_MAX_LOW	0x08
+#define MSC313E_REG_TIMER_MAX_HIGH	0x0c
+#define MSC313E_REG_COUNTER_LOW		0x10
+#define MSC313E_REG_COUNTER_HIGH	0x14
+#define MSC313E_REG_TIMER_DIVIDE	0x18
+
+#define MSC313E_CLK_DIVIDER		9
+#define TIMER_SYNC_TICKS		3
+
+#ifdef CONFIG_ARM
+struct msc313e_delay {
+	void __iomem *base;
+	struct delay_timer delay;
+};
+static struct msc313e_delay msc313e_delay;
+#endif
+
+static void __iomem *msc313e_clksrc;
+
+static void msc313e_timer_stop(void __iomem *base)
+{
+	writew(0, base + MSC313E_REG_CTRL);
+}
+
+static void msc313e_timer_start(void __iomem *base, bool periodic)
+{
+	u16 reg;
+
+	reg = readw(base + MSC313E_REG_CTRL);
+	if (periodic)
+		reg |= MSC313E_REG_CTRL_TIMER_EN;
+	else
+		reg |= MSC313E_REG_CTRL_TIMER_TRIG;
+	writew(reg | MSC313E_REG_CTRL_TIMER_INT_EN, base + MSC313E_REG_CTRL);
+}
+
+static void msc313e_timer_setup(void __iomem *base, unsigned long delay)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	writew(delay >> 16, base + MSC313E_REG_TIMER_MAX_HIGH);
+	writew(delay & 0xffff, base + MSC313E_REG_TIMER_MAX_LOW);
+	local_irq_restore(flags);
+}
+
+static unsigned long msc313e_timer_current_value(void __iomem *base)
+{
+	unsigned long flags;
+	u16 l, h;
+
+	local_irq_save(flags);
+	l = readw(base + MSC313E_REG_COUNTER_LOW);
+	h = readw(base + MSC313E_REG_COUNTER_HIGH);
+	local_irq_restore(flags);
+
+	return (((u32)h) << 16 | l);
+}
+
+static int msc313e_timer_clkevt_shutdown(struct clock_event_device *evt)
+{
+	struct timer_of *timer = to_timer_of(evt);
+
+	msc313e_timer_stop(timer_of_base(timer));
+
+	return 0;
+}
+
+static int msc313e_timer_clkevt_set_oneshot(struct clock_event_device *evt)
+{
+	struct timer_of *timer = to_timer_of(evt);
+
+	msc313e_timer_stop(timer_of_base(timer));
+	msc313e_timer_start(timer_of_base(timer), false);
+
+	return 0;
+}
+
+static int msc313e_timer_clkevt_set_periodic(struct clock_event_device *evt)
+{
+	struct timer_of *timer = to_timer_of(evt);
+
+	msc313e_timer_stop(timer_of_base(timer));
+	msc313e_timer_setup(timer_of_base(timer), timer_of_period(timer));
+	msc313e_timer_start(timer_of_base(timer), true);
+
+	return 0;
+}
+
+static int msc313e_timer_clkevt_next_event(unsigned long evt, struct clock_event_device *clkevt)
+{
+	struct timer_of *timer = to_timer_of(clkevt);
+
+	msc313e_timer_stop(timer_of_base(timer));
+	msc313e_timer_setup(timer_of_base(timer), evt);
+	msc313e_timer_start(timer_of_base(timer), false);
+
+	return 0;
+}
+
+static irqreturn_t msc313e_timer_clkevt_irq(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = dev_id;
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+static u64 msc313e_timer_clksrc_read(struct clocksource *cs)
+{
+	return msc313e_timer_current_value(msc313e_clksrc) & cs->mask;
+}
+
+#ifdef CONFIG_ARM
+static unsigned long msc313e_read_delay_timer_read(void)
+{
+	return msc313e_timer_current_value(msc313e_delay.base);
+}
+#endif
+
+static u64 msc313e_timer_sched_clock_read(void)
+{
+	return msc313e_timer_current_value(msc313e_clksrc);
+}
+
+static struct clock_event_device msc313e_clkevt = {
+	.name = TIMER_NAME,
+	.rating = 300,
+	.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_shutdown = msc313e_timer_clkevt_shutdown,
+	.set_state_periodic = msc313e_timer_clkevt_set_periodic,
+	.set_state_oneshot = msc313e_timer_clkevt_set_oneshot,
+	.tick_resume = msc313e_timer_clkevt_shutdown,
+	.set_next_event = msc313e_timer_clkevt_next_event,
+};
+
+static int __init msc313e_clkevt_init(struct device_node *np)
+{
+	int ret;
+	struct timer_of *to;
+
+	to = kzalloc_obj(*to);
+	if (!to)
+		return -ENOMEM;
+
+	to->flags = TIMER_OF_IRQ | TIMER_OF_CLOCK | TIMER_OF_BASE;
+	to->of_irq.handler = msc313e_timer_clkevt_irq;
+	ret = timer_of_init(np, to);
+	if (ret)
+		return ret;
+
+	if (of_device_is_compatible(np, "sstar,ssd20xd-timer")) {
+		to->of_clk.rate = clk_get_rate(to->of_clk.clk) / MSC313E_CLK_DIVIDER;
+		to->of_clk.period = DIV_ROUND_UP(to->of_clk.rate, HZ);
+		writew(MSC313E_CLK_DIVIDER - 1, timer_of_base(to) + MSC313E_REG_TIMER_DIVIDE);
+	}
+
+	msc313e_clkevt.cpumask = cpu_possible_mask;
+	msc313e_clkevt.irq = to->of_irq.irq;
+	to->clkevt = msc313e_clkevt;
+
+	clockevents_config_and_register(&to->clkevt, timer_of_rate(to),
+					TIMER_SYNC_TICKS, 0xffffffff);
+	return 0;
+}
+
+static int __init msc313e_clksrc_init(struct device_node *np)
+{
+	struct timer_of to = { 0 };
+	int ret;
+	u16 reg;
+
+	to.flags = TIMER_OF_BASE | TIMER_OF_CLOCK;
+	ret = timer_of_init(np, &to);
+	if (ret)
+		return ret;
+
+	msc313e_clksrc = timer_of_base(&to);
+	reg = readw(msc313e_clksrc + MSC313E_REG_CTRL);
+	reg |= MSC313E_REG_CTRL_TIMER_EN;
+	writew(reg, msc313e_clksrc + MSC313E_REG_CTRL);
+
+#ifdef CONFIG_ARM
+	msc313e_delay.base = timer_of_base(&to);
+	msc313e_delay.delay.read_current_timer = msc313e_read_delay_timer_read;
+	msc313e_delay.delay.freq = timer_of_rate(&to);
+
+	register_current_timer_delay(&msc313e_delay.delay);
+#endif
+
+	sched_clock_register(msc313e_timer_sched_clock_read, 32, timer_of_rate(&to));
+	return clocksource_mmio_init(timer_of_base(&to), TIMER_NAME, timer_of_rate(&to), 300, 32,
+				     msc313e_timer_clksrc_read);
+}
+
+static int __init msc313e_timer_init(struct device_node *np)
+{
+	int ret = 0;
+	static int num_called;
+
+	switch (num_called) {
+	case 0:
+		ret = msc313e_clksrc_init(np);
+		if (ret)
+			return ret;
+		break;
+
+	default:
+		ret = msc313e_clkevt_init(np);
+		if (ret)
+			return ret;
+		break;
+	}
+
+	num_called++;
+
+	return 0;
+}
+
+TIMER_OF_DECLARE(msc313, "mstar,msc313e-timer", msc313e_timer_init);
+TIMER_OF_DECLARE(ssd20xd, "sstar,ssd20xd-timer", msc313e_timer_init);