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");
141