1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Slim Bootloader(SBL) firmware update signaling driver
  4 *
  5 * Slim Bootloader is a small, open-source, non UEFI compliant, boot firmware
  6 * optimized for running on certain Intel platforms.
  7 *
  8 * SBL exposes an ACPI-WMI device via /sys/bus/wmi/devices/<INTEL_WMI_SBL_GUID>.
  9 * This driver further adds "firmware_update_request" device attribute.
 10 * This attribute normally has a value of 0 and userspace can signal SBL
 11 * to update firmware, on next reboot, by writing a value of 1.
 12 *
 13 * More details of SBL firmware update process is available at:
 14 * https://slimbootloader.github.io/security/firmware-update.html
 15 */
 16
 17#include <linux/acpi.h>
 18#include <linux/device.h>
 19#include <linux/module.h>
 20#include <linux/slab.h>
 21#include <linux/sysfs.h>
 22#include <linux/wmi.h>
 23
 24#define INTEL_WMI_SBL_GUID  "44FADEB1-B204-40F2-8581-394BBDC1B651"
 25
 26static int get_fwu_request(struct device *dev, u32 *out)
 27{
 28	union acpi_object *obj;
 29
 30	obj = wmidev_block_query(to_wmi_device(dev), 0);
 31	if (!obj)
 32		return -ENODEV;
 33
 34	if (obj->type != ACPI_TYPE_INTEGER) {
 35		dev_warn(dev, "wmidev_block_query returned invalid value\n");
 36		kfree(obj);
 37		return -EINVAL;
 38	}
 39
 40	*out = obj->integer.value;
 41	kfree(obj);
 42
 43	return 0;
 44}
 45
 46static int set_fwu_request(struct device *dev, u32 in)
 47{
 48	struct acpi_buffer input;
 49	acpi_status status;
 50	u32 value;
 51
 52	value = in;
 53	input.length = sizeof(u32);
 54	input.pointer = &value;
 55
 56	status = wmidev_block_set(to_wmi_device(dev), 0, &input);
 57	if (ACPI_FAILURE(status)) {
 58		dev_err(dev, "wmidev_block_set failed\n");
 59		return -ENODEV;
 60	}
 61
 62	return 0;
 63}
 64
 65static ssize_t firmware_update_request_show(struct device *dev,
 66					    struct device_attribute *attr,
 67					    char *buf)
 68{
 69	u32 val;
 70	int ret;
 71
 72	ret = get_fwu_request(dev, &val);
 73	if (ret)
 74		return ret;
 75
 76	return sprintf(buf, "%d\n", val);
 77}
 78
 79static ssize_t firmware_update_request_store(struct device *dev,
 80					     struct device_attribute *attr,
 81					     const char *buf, size_t count)
 82{
 83	unsigned int val;
 84	int ret;
 85
 86	ret = kstrtouint(buf, 0, &val);
 87	if (ret)
 88		return ret;
 89
 90	/* May later be extended to support values other than 0 and 1 */
 91	if (val > 1)
 92		return -ERANGE;
 93
 94	ret = set_fwu_request(dev, val);
 95	if (ret)
 96		return ret;
 97
 98	return count;
 99}
100static DEVICE_ATTR_RW(firmware_update_request);
101
102static struct attribute *firmware_update_attrs[] = {
103	&dev_attr_firmware_update_request.attr,
104	NULL
105};
106ATTRIBUTE_GROUPS(firmware_update);
107
108static int intel_wmi_sbl_fw_update_probe(struct wmi_device *wdev,
109					 const void *context)
110{
111	dev_info(&wdev->dev, "Slim Bootloader signaling driver attached\n");
112	return 0;
113}
114
115static void intel_wmi_sbl_fw_update_remove(struct wmi_device *wdev)
116{
117	dev_info(&wdev->dev, "Slim Bootloader signaling driver removed\n");
118}
119
120static const struct wmi_device_id intel_wmi_sbl_id_table[] = {
121	{ .guid_string = INTEL_WMI_SBL_GUID },
122	{}
123};
124MODULE_DEVICE_TABLE(wmi, intel_wmi_sbl_id_table);
125
126static struct wmi_driver intel_wmi_sbl_fw_update_driver = {
127	.driver = {
128		.name = "intel-wmi-sbl-fw-update",
129		.dev_groups = firmware_update_groups,
130	},
131	.probe = intel_wmi_sbl_fw_update_probe,
132	.remove = intel_wmi_sbl_fw_update_remove,
133	.id_table = intel_wmi_sbl_id_table,
134	.no_singleton = true,
135};
136module_wmi_driver(intel_wmi_sbl_fw_update_driver);
137
138MODULE_AUTHOR("Jithu Joseph <jithu.joseph@intel.com>");
139MODULE_DESCRIPTION("Slim Bootloader firmware update signaling driver");
140MODULE_LICENSE("GPL v2");