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, 120 insertions, 0 deletions

diff --git a/drivers/net/phy/amd.c b/drivers/net/phy/amd.c
new file mode 100644
index 000000000..75b5fe655
--- /dev/null
+++ b/drivers/net/phy/amd.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for AMD am79c PHYs
+ *
+ * Author: Heiko Schocher <hs@denx.de>
+ *
+ * Copyright (c) 2011 DENX Software Engineering GmbH
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mii.h>
+#include <linux/phy.h>
+
+#define PHY_ID_AC101L		0x00225520
+#define PHY_ID_AM79C874		0x0022561b
+
+#define MII_AM79C_IR		17	/* Interrupt Status/Control Register */
+#define MII_AM79C_IR_EN_LINK	0x0400	/* IR enable Linkstate */
+#define MII_AM79C_IR_EN_ANEG	0x0100	/* IR enable Aneg Complete */
+#define MII_AM79C_IR_IMASK_INIT	(MII_AM79C_IR_EN_LINK | MII_AM79C_IR_EN_ANEG)
+
+#define MII_AM79C_IR_LINK_DOWN	BIT(2)
+#define MII_AM79C_IR_ANEG_DONE	BIT(0)
+#define MII_AM79C_IR_IMASK_STAT	(MII_AM79C_IR_LINK_DOWN | MII_AM79C_IR_ANEG_DONE)
+
+MODULE_DESCRIPTION("AMD PHY driver");
+MODULE_AUTHOR("Heiko Schocher <hs@denx.de>");
+MODULE_LICENSE("GPL");
+
+static int am79c_ack_interrupt(struct phy_device *phydev)
+{
+	int err;
+
+	err = phy_read(phydev, MII_BMSR);
+	if (err < 0)
+		return err;
+
+	err = phy_read(phydev, MII_AM79C_IR);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int am79c_config_init(struct phy_device *phydev)
+{
+	return 0;
+}
+
+static int am79c_config_intr(struct phy_device *phydev)
+{
+	int err;
+
+	if (phydev->interrupts == PHY_INTERRUPT_ENABLED) {
+		err = am79c_ack_interrupt(phydev);
+		if (err)
+			return err;
+
+		err = phy_write(phydev, MII_AM79C_IR, MII_AM79C_IR_IMASK_INIT);
+	} else {
+		err = phy_write(phydev, MII_AM79C_IR, 0);
+		if (err)
+			return err;
+
+		err = am79c_ack_interrupt(phydev);
+	}
+
+	return err;
+}
+
+static irqreturn_t am79c_handle_interrupt(struct phy_device *phydev)
+{
+	int irq_status;
+
+	irq_status = phy_read(phydev, MII_AM79C_IR);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	if (!(irq_status & MII_AM79C_IR_IMASK_STAT))
+		return IRQ_NONE;
+
+	phy_trigger_machine(phydev);
+
+	return IRQ_HANDLED;
+}
+
+static struct phy_driver am79c_drivers[] = {
+	{
+		.phy_id		= PHY_ID_AM79C874,
+		.name		= "AM79C874",
+		.phy_id_mask	= 0xfffffff0,
+		/* PHY_BASIC_FEATURES */
+		.config_init	= am79c_config_init,
+		.config_intr	= am79c_config_intr,
+		.handle_interrupt = am79c_handle_interrupt,
+	},
+	{
+		.phy_id		= PHY_ID_AC101L,
+		.name		= "AC101L",
+		.phy_id_mask	= 0xfffffff0,
+		/* PHY_BASIC_FEATURES */
+		.config_init	= am79c_config_init,
+		.config_intr	= am79c_config_intr,
+		.handle_interrupt = am79c_handle_interrupt,
+	},
+};
+
+module_phy_driver(am79c_drivers);
+
+static const struct mdio_device_id __maybe_unused amd_tbl[] = {
+	{ PHY_ID_AC101L, 0xfffffff0 },
+	{ PHY_ID_AM79C874, 0xfffffff0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(mdio, amd_tbl);