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	struct acpi_buffer result = {ACPI_ALLOCATE_BUFFER, NULL};
29	union acpi_object *obj;
30	acpi_status status;
31
32	status = wmi_query_block(INTEL_WMI_SBL_GUID, 0, &result);
33	if (ACPI_FAILURE(status)) {
34		dev_err(dev, "wmi_query_block failed\n");
35		return -ENODEV;
36	}
37
38	obj = (union acpi_object *)result.pointer;
39	if (!obj || obj->type != ACPI_TYPE_INTEGER) {
40		dev_warn(dev, "wmi_query_block returned invalid value\n");
41		kfree(obj);
42		return -EINVAL;
43	}
44
45	*out = obj->integer.value;
46	kfree(obj);
47
48	return 0;
49}
50
51static int set_fwu_request(struct device *dev, u32 in)
52{
53	struct acpi_buffer input;
54	acpi_status status;
55	u32 value;
56
57	value = in;
58	input.length = sizeof(u32);
59	input.pointer = &value;
60
61	status = wmi_set_block(INTEL_WMI_SBL_GUID, 0, &input);
62	if (ACPI_FAILURE(status)) {
63		dev_err(dev, "wmi_set_block failed\n");
64		return -ENODEV;
65	}
66
67	return 0;
68}
69
70static ssize_t firmware_update_request_show(struct device *dev,
71					    struct device_attribute *attr,
72					    char *buf)
73{
74	u32 val;
75	int ret;
76
77	ret = get_fwu_request(dev, &val);
78	if (ret)
79		return ret;
80
81	return sprintf(buf, "%d\n", val);
82}
83
84static ssize_t firmware_update_request_store(struct device *dev,
85					     struct device_attribute *attr,
86					     const char *buf, size_t count)
87{
88	unsigned int val;
89	int ret;
90
91	ret = kstrtouint(buf, 0, &val);
92	if (ret)
93		return ret;
94
95	/* May later be extended to support values other than 0 and 1 */
96	if (val > 1)
97		return -ERANGE;
98
99	ret = set_fwu_request(dev, val);
100	if (ret)
101		return ret;
102
103	return count;
104}
105static DEVICE_ATTR_RW(firmware_update_request);
106
107static struct attribute *firmware_update_attrs[] = {
108	&dev_attr_firmware_update_request.attr,
109	NULL
110};
111ATTRIBUTE_GROUPS(firmware_update);
112
113static int intel_wmi_sbl_fw_update_probe(struct wmi_device *wdev,
114					 const void *context)
115{
116	dev_info(&wdev->dev, "Slim Bootloader signaling driver attached\n");
117	return 0;
118}
119
120static void intel_wmi_sbl_fw_update_remove(struct wmi_device *wdev)
121{
122	dev_info(&wdev->dev, "Slim Bootloader signaling driver removed\n");
123}
124
125static const struct wmi_device_id intel_wmi_sbl_id_table[] = {
126	{ .guid_string = INTEL_WMI_SBL_GUID },
127	{}
128};
129MODULE_DEVICE_TABLE(wmi, intel_wmi_sbl_id_table);
130
131static struct wmi_driver intel_wmi_sbl_fw_update_driver = {
132	.driver = {
133		.name = "intel-wmi-sbl-fw-update",
134		.dev_groups = firmware_update_groups,
135	},
136	.probe = intel_wmi_sbl_fw_update_probe,
137	.remove = intel_wmi_sbl_fw_update_remove,
138	.id_table = intel_wmi_sbl_id_table,
139};
140module_wmi_driver(intel_wmi_sbl_fw_update_driver);
141
142MODULE_AUTHOR("Jithu Joseph <jithu.joseph@intel.com>");
143MODULE_DESCRIPTION("Slim Bootloader firmware update signaling driver");
144MODULE_LICENSE("GPL v2");
145