firewall: introduce stm32_firewall framework

Introduce a STM32 firewall framework that offers to firewall consumers
different firewall services such as the ability to check their access
rights against their firewall controller(s).

The STM32 firewall framework offers a generic API for STM32 firewall
controllers that is defined in their drivers to best fit the
specificity of each firewall.

There are various types of firewalls:
-Peripheral firewalls that filter accesses to peripherals
-Memory firewalls that filter accesses to memories or memory regions
-No type for undefined type of firewall

Signed-off-by: Gatien Chevallier <[e-mail]>
Signed-off-by: Alexandre Torgue <[e-mail]>

MAINTAINERS

···
 F:	Documentation/devicetree/bindings/media/i2c/st,st-mipid02.yaml
 F:	drivers/media/i2c/st-mipid02.c
 
+ST STM32 FIREWALL
+M:	Gatien Chevallier <[e-mail]>
+S:	Maintained
+F:	drivers/bus/stm32_firewall.c
+
 ST STM32 I2C/SMBUS DRIVER
 M:	Pierre-Yves MORDRET <[e-mail]>
 M:	Alain Volmat <[e-mail]>

arch/arm/mach-stm32/Kconfig

···
 	select PINCTRL
 	select RESET_CONTROLLER
 	select STM32_EXTI
+	select STM32_FIREWALL
 	help
 	  Support for STMicroelectronics STM32 processors.
 

arch/arm64/Kconfig.platforms

···
 	select ARM_SMC_MBOX
 	select ARM_SCMI_PROTOCOL
 	select COMMON_CLK_SCMI
+	select STM32_FIREWALL
 	help
 	  This enables support for ARMv8 based STMicroelectronics
 	  STM32 family, including:

drivers/bus/Kconfig

···
 	  i2c/spi/uart controllers, a hexagon core, and a clock controller
 	  which provides clocks for the above.
 
+config STM32_FIREWALL
+	bool "STM32 Firewall framework"
+	depends on (ARCH_STM32 || COMPILE_TEST) && OF
+	select OF_DYNAMIC
+	help
+	  Say y to enable STM32 firewall framework and its services. Firewall
+	  controllers will be able to register to the framework. Access for
+	  hardware resources linked to a firewall controller can be requested
+	  through this STM32 framework.
+
 config SUN50I_DE2_BUS
 	bool "Allwinner A64 DE2 Bus Driver"
 	  default ARM64

drivers/bus/Makefile

···
 obj-$(CONFIG_OMAP_OCP2SCP)	+= omap-ocp2scp.o
 obj-$(CONFIG_QCOM_EBI2)		+= qcom-ebi2.o
 obj-$(CONFIG_QCOM_SSC_BLOCK_BUS)	+= qcom-ssc-block-bus.o
+obj-$(CONFIG_STM32_FIREWALL)	+= stm32_firewall.o
 obj-$(CONFIG_SUN50I_DE2_BUS)	+= sun50i-de2.o
 obj-$(CONFIG_SUNXI_RSB)		+= sunxi-rsb.o
 obj-$(CONFIG_OF)		+= simple-pm-bus.o

drivers/bus/stm32_firewall.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
+ */
+
+#include <linux/bitfield.h>
+#include <linux/bits.h>
+#include <linux/bus/stm32_firewall_device.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+
+#include "stm32_firewall.h"
+
+/* Corresponds to STM32_FIREWALL_MAX_EXTRA_ARGS + firewall ID */
+#define STM32_FIREWALL_MAX_ARGS		(STM32_FIREWALL_MAX_EXTRA_ARGS + 1)
+
+static LIST_HEAD(firewall_controller_list);
+static DEFINE_MUTEX(firewall_controller_list_lock);
+
+/* Firewall device API */
+
+int stm32_firewall_get_firewall(struct device_node *np, struct stm32_firewall *firewall,
+				unsigned int nb_firewall)
+{
+	struct stm32_firewall_controller *ctrl;
+	struct of_phandle_iterator it;
+	unsigned int i, j = 0;
+	int err;
+
+	if (!firewall || !nb_firewall)
+		return -EINVAL;
+
+	/* Parse property with phandle parsed out */
+	of_for_each_phandle(&it, err, np, "access-controllers", "#access-controller-cells", 0) {
+		struct of_phandle_args provider_args;
+		struct device_node *provider = it.node;
+		const char *fw_entry;
+		bool match = false;
+
+		if (err) {
+			pr_err("Unable to get access-controllers property for node %s\n, err: %d",
+			       np->full_name, err);
+			of_node_put(provider);
+			return err;
+		}
+
+		if (j > nb_firewall) {
+			pr_err("Too many firewall controllers");
+			of_node_put(provider);
+			return -EINVAL;
+		}
+
+		provider_args.args_count = of_phandle_iterator_args(&it, provider_args.args,
+								    STM32_FIREWALL_MAX_ARGS);
+
+		/* Check if the parsed phandle corresponds to a registered firewall controller */
+		mutex_lock(&firewall_controller_list_lock);
+		list_for_each_entry(ctrl, &firewall_controller_list, entry) {
+			if (ctrl->dev->of_node->phandle == it.phandle) {
+				match = true;
+				firewall[j].firewall_ctrl = ctrl;
+				break;
+			}
+		}
+		mutex_unlock(&firewall_controller_list_lock);
+
+		if (!match) {
+			firewall[j].firewall_ctrl = NULL;
+			pr_err("No firewall controller registered for %s\n", np->full_name);
+			of_node_put(provider);
+			return -ENODEV;
+		}
+
+		err = of_property_read_string_index(np, "access-controller-names", j, &fw_entry);
+		if (err == 0)
+			firewall[j].entry = fw_entry;
+
+		/* Handle the case when there are no arguments given along with the phandle */
+		if (provider_args.args_count < 0 ||
+		    provider_args.args_count > STM32_FIREWALL_MAX_ARGS) {
+			of_node_put(provider);
+			return -EINVAL;
+		} else if (provider_args.args_count == 0) {
+			firewall[j].extra_args_size = 0;
+			firewall[j].firewall_id = U32_MAX;
+			j++;
+			continue;
+		}
+
+		/* The firewall ID is always the first argument */
+		firewall[j].firewall_id = provider_args.args[0];
+
+		/* Extra args start at the second argument */
+		for (i = 0; i < provider_args.args_count - 1; i++)
+			firewall[j].extra_args[i] = provider_args.args[i + 1];
+
+		/* Remove the firewall ID arg that is not an extra argument */
+		firewall[j].extra_args_size = provider_args.args_count - 1;
+
+		j++;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_get_firewall);
+
+int stm32_firewall_grant_access(struct stm32_firewall *firewall)
+{
+	struct stm32_firewall_controller *firewall_controller;
+
+	if (!firewall || firewall->firewall_id == U32_MAX)
+		return -EINVAL;
+
+	firewall_controller = firewall->firewall_ctrl;
+
+	if (!firewall_controller)
+		return -ENODEV;
+
+	return firewall_controller->grant_access(firewall_controller, firewall->firewall_id);
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_grant_access);
+
+int stm32_firewall_grant_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id)
+{
+	struct stm32_firewall_controller *firewall_controller;
+
+	if (!firewall || subsystem_id == U32_MAX || firewall->firewall_id == U32_MAX)
+		return -EINVAL;
+
+	firewall_controller = firewall->firewall_ctrl;
+
+	if (!firewall_controller)
+		return -ENODEV;
+
+	return firewall_controller->grant_access(firewall_controller, subsystem_id);
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_grant_access_by_id);
+
+void stm32_firewall_release_access(struct stm32_firewall *firewall)
+{
+	struct stm32_firewall_controller *firewall_controller;
+
+	if (!firewall || firewall->firewall_id == U32_MAX) {
+		pr_debug("Incorrect arguments when releasing a firewall access\n");
+		return;
+	}
+
+	firewall_controller = firewall->firewall_ctrl;
+
+	if (!firewall_controller) {
+		pr_debug("No firewall controller to release\n");
+		return;
+	}
+
+	firewall_controller->release_access(firewall_controller, firewall->firewall_id);
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_release_access);
+
+void stm32_firewall_release_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id)
+{
+	struct stm32_firewall_controller *firewall_controller;
+
+	if (!firewall || subsystem_id == U32_MAX || firewall->firewall_id == U32_MAX) {
+		pr_debug("Incorrect arguments when releasing a firewall access");
+		return;
+	}
+
+	firewall_controller = firewall->firewall_ctrl;
+
+	if (!firewall_controller) {
+		pr_debug("No firewall controller to release");
+		return;
+	}
+
+	firewall_controller->release_access(firewall_controller, subsystem_id);
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_release_access_by_id);
+
+/* Firewall controller API */
+
+int stm32_firewall_controller_register(struct stm32_firewall_controller *firewall_controller)
+{
+	struct stm32_firewall_controller *ctrl;
+
+	if (!firewall_controller)
+		return -ENODEV;
+
+	pr_info("Registering %s firewall controller\n", firewall_controller->name);
+
+	mutex_lock(&firewall_controller_list_lock);
+	list_for_each_entry(ctrl, &firewall_controller_list, entry) {
+		if (ctrl == firewall_controller) {
+			pr_debug("%s firewall controller already registered\n",
+				 firewall_controller->name);
+			mutex_unlock(&firewall_controller_list_lock);
+			return 0;
+		}
+	}
+	list_add_tail(&firewall_controller->entry, &firewall_controller_list);
+	mutex_unlock(&firewall_controller_list_lock);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_controller_register);
+
+void stm32_firewall_controller_unregister(struct stm32_firewall_controller *firewall_controller)
+{
+	struct stm32_firewall_controller *ctrl;
+	bool controller_removed = false;
+
+	if (!firewall_controller) {
+		pr_debug("Null reference while unregistering firewall controller\n");
+		return;
+	}
+
+	mutex_lock(&firewall_controller_list_lock);
+	list_for_each_entry(ctrl, &firewall_controller_list, entry) {
+		if (ctrl == firewall_controller) {
+			controller_removed = true;
+			list_del_init(&ctrl->entry);
+			break;
+		}
+	}
+	mutex_unlock(&firewall_controller_list_lock);
+
+	if (!controller_removed)
+		pr_debug("There was no firewall controller named %s to unregister\n",
+			 firewall_controller->name);
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_controller_unregister);
+
+int stm32_firewall_populate_bus(struct stm32_firewall_controller *firewall_controller)
+{
+	struct stm32_firewall *firewalls;
+	struct device_node *child;
+	struct device *parent;
+	unsigned int i;
+	int len;
+	int err;
+
+	parent = firewall_controller->dev;
+
+	dev_dbg(parent, "Populating %s system bus\n", dev_name(firewall_controller->dev));
+
+	for_each_available_child_of_node(dev_of_node(parent), child) {
+		/* The access-controllers property is mandatory for firewall bus devices */
+		len = of_count_phandle_with_args(child, "access-controllers",
+						 "#access-controller-cells");
+		if (len <= 0) {
+			of_node_put(child);
+			return -EINVAL;
+		}
+
+		firewalls = kcalloc(len, sizeof(*firewalls), GFP_KERNEL);
+		if (!firewalls) {
+			of_node_put(child);
+			return -ENOMEM;
+		}
+
+		err = stm32_firewall_get_firewall(child, firewalls, (unsigned int)len);
+		if (err) {
+			kfree(firewalls);
+			of_node_put(child);
+			return err;
+		}
+
+		for (i = 0; i < len; i++) {
+			if (firewall_controller->grant_access(firewall_controller,
+							      firewalls[i].firewall_id)) {
+				/*
+				 * Peripheral access not allowed or not defined.
+				 * Mark the node as populated so platform bus won't probe it
+				 */
+				of_detach_node(child);
+				dev_err(parent, "%s: Device driver will not be probed\n",
+					child->full_name);
+			}
+		}
+
+		kfree(firewalls);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(stm32_firewall_populate_bus);

drivers/bus/stm32_firewall.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
+ */
+
+#ifndef _STM32_FIREWALL_H
+#define _STM32_FIREWALL_H
+
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+/**
+ * STM32_PERIPHERAL_FIREWALL:		This type of firewall protects peripherals
+ * STM32_MEMORY_FIREWALL:		This type of firewall protects memories/subsets of memory
+ *					zones
+ * STM32_NOTYPE_FIREWALL:		Undefined firewall type
+ */
+
+#define STM32_PERIPHERAL_FIREWALL	BIT(1)
+#define STM32_MEMORY_FIREWALL		BIT(2)
+#define STM32_NOTYPE_FIREWALL		BIT(3)
+
+/**
+ * struct stm32_firewall_controller - Information on firewall controller supplying services
+ *
+ * @name:			Name of the firewall controller
+ * @dev:			Device reference of the firewall controller
+ * @mmio:			Base address of the firewall controller
+ * @entry:			List entry of the firewall controller list
+ * @type:			Type of firewall
+ * @max_entries:		Number of entries covered by the firewall
+ * @grant_access:		Callback used to grant access for a device access against a
+ *				firewall controller
+ * @release_access:		Callback used to release resources taken by a device when access was
+ *				granted
+ * @grant_memory_range_access:	Callback used to grant access for a device to a given memory region
+ */
+struct stm32_firewall_controller {
+	const char *name;
+	struct device *dev;
+	void __iomem *mmio;
+	struct list_head entry;
+	unsigned int type;
+	unsigned int max_entries;
+
+	int (*grant_access)(struct stm32_firewall_controller *ctrl, u32 id);
+	void (*release_access)(struct stm32_firewall_controller *ctrl, u32 id);
+	int (*grant_memory_range_access)(struct stm32_firewall_controller *ctrl, phys_addr_t paddr,
+					 size_t size);
+};
+
+/**
+ * stm32_firewall_controller_register - Register a firewall controller to the STM32 firewall
+ *					framework
+ * @firewall_controller:	Firewall controller to register
+ *
+ * Returns 0 in case of success or -ENODEV if no controller was given.
+ */
+int stm32_firewall_controller_register(struct stm32_firewall_controller *firewall_controller);
+
+/**
+ * stm32_firewall_controller_unregister - Unregister a firewall controller from the STM32
+ *					  firewall framework
+ * @firewall_controller:	Firewall controller to unregister
+ */
+void stm32_firewall_controller_unregister(struct stm32_firewall_controller *firewall_controller);
+
+/**
+ * stm32_firewall_populate_bus - Populate device tree nodes that have a correct firewall
+ *				 configuration. This is used at boot-time only, as a sanity check
+ *				 between device tree and firewalls hardware configurations to
+ *				 prevent a kernel crash when a device driver is not granted access
+ *
+ * @firewall_controller:	Firewall controller which nodes will be populated or not
+ *
+ * Returns 0 in case of success or appropriate errno code if error occurred.
+ */
+int stm32_firewall_populate_bus(struct stm32_firewall_controller *firewall_controller);
+
+#endif /* _STM32_FIREWALL_H */

include/linux/bus/stm32_firewall_device.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
+ */
+
+#ifndef STM32_FIREWALL_DEVICE_H
+#define STM32_FIREWALL_DEVICE_H
+
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#define STM32_FIREWALL_MAX_EXTRA_ARGS		5
+
+/* Opaque reference to stm32_firewall_controller */
+struct stm32_firewall_controller;
+
+/**
+ * struct stm32_firewall - Information on a device's firewall. Each device can have more than one
+ *			   firewall.
+ *
+ * @firewall_ctrl:		Pointer referencing a firewall controller of the device. It is
+ *				opaque so a device cannot manipulate the controller's ops or access
+ *				the controller's data
+ * @extra_args:			Extra arguments that are implementation dependent
+ * @entry:			Name of the firewall entry
+ * @extra_args_size:		Number of extra arguments
+ * @firewall_id:		Firewall ID associated the device for this firewall controller
+ */
+struct stm32_firewall {
+	struct stm32_firewall_controller *firewall_ctrl;
+	u32 extra_args[STM32_FIREWALL_MAX_EXTRA_ARGS];
+	const char *entry;
+	size_t extra_args_size;
+	u32 firewall_id;
+};
+
+#if IS_ENABLED(CONFIG_STM32_FIREWALL)
+/**
+ * stm32_firewall_get_firewall - Get the firewall(s) associated to given device.
+ *				 The firewall controller reference is always the first argument
+ *				 of each of the access-controller property entries.
+ *				 The firewall ID is always the second argument of each of the
+ *				 access-controller  property entries.
+ *				 If there's no argument linked to the phandle, then the firewall ID
+ *				 field is set to U32_MAX, which is an invalid ID.
+ *
+ * @np:				Device node to parse
+ * @firewall:			Array of firewall references
+ * @nb_firewall:		Number of firewall references to get. Must be at least 1.
+ *
+ * Returns 0 on success, -ENODEV if there's no match with a firewall controller or appropriate errno
+ * code if error occurred.
+ */
+int stm32_firewall_get_firewall(struct device_node *np, struct stm32_firewall *firewall,
+				unsigned int nb_firewall);
+
+/**
+ * stm32_firewall_grant_access - Request firewall access rights and grant access.
+ *
+ * @firewall:			Firewall reference containing the ID to check against its firewall
+ *				controller
+ *
+ * Returns 0 if access is granted, -EACCES if access is denied, -ENODEV if firewall is null or
+ * appropriate errno code if error occurred
+ */
+int stm32_firewall_grant_access(struct stm32_firewall *firewall);
+
+/**
+ * stm32_firewall_release_access - Release access granted from a call to
+ *				   stm32_firewall_grant_access().
+ *
+ * @firewall:			Firewall reference containing the ID to check against its firewall
+ *				controller
+ */
+void stm32_firewall_release_access(struct stm32_firewall *firewall);
+
+/**
+ * stm32_firewall_grant_access_by_id - Request firewall access rights of a given device
+ *				       based on a specific firewall ID
+ *
+ * Warnings:
+ * There is no way to ensure that the given ID will correspond to the firewall referenced in the
+ * device node if the ID did not come from stm32_firewall_get_firewall(). In that case, this
+ * function must be used with caution.
+ * This function should be used for subsystem resources that do not have the same firewall ID
+ * as their parent.
+ * U32_MAX is an invalid ID.
+ *
+ * @firewall:			Firewall reference containing the firewall controller
+ * @subsystem_id:		Firewall ID of the subsystem resource
+ *
+ * Returns 0 if access is granted, -EACCES if access is denied, -ENODEV if firewall is null or
+ * appropriate errno code if error occurred
+ */
+int stm32_firewall_grant_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id);
+
+/**
+ * stm32_firewall_release_access_by_id - Release access granted from a call to
+ *					 stm32_firewall_grant_access_by_id().
+ *
+ * Warnings:
+ * There is no way to ensure that the given ID will correspond to the firewall referenced in the
+ * device node if the ID did not come from stm32_firewall_get_firewall(). In that case, this
+ * function must be used with caution.
+ * This function should be used for subsystem resources that do not have the same firewall ID
+ * as their parent.
+ * U32_MAX is an invalid ID.
+ *
+ * @firewall:			Firewall reference containing the firewall controller
+ * @subsystem_id:		Firewall ID of the subsystem resource
+ */
+void stm32_firewall_release_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id);
+
+#else /* CONFIG_STM32_FIREWALL */
+
+int stm32_firewall_get_firewall(struct device_node *np, struct stm32_firewall *firewall,
+				unsigned int nb_firewall);
+{
+	return -ENODEV;
+}
+
+int stm32_firewall_grant_access(struct stm32_firewall *firewall)
+{
+	return -ENODEV;
+}
+
+void stm32_firewall_release_access(struct stm32_firewall *firewall)
+{
+}
+
+int stm32_firewall_grant_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id)
+{
+	return -ENODEV;
+}
+
+void stm32_firewall_release_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id)
+{
+}
+
+#endif /* CONFIG_STM32_FIREWALL */
+#endif /* STM32_FIREWALL_DEVICE_H */