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 
26 static 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 
51 static 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 
70 static 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 
84 static 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 }
105 static DEVICE_ATTR_RW(firmware_update_request);
106 
107 static struct attribute *firmware_update_attrs[] = {
108 	&dev_attr_firmware_update_request.attr,
109 	NULL
110 };
111 ATTRIBUTE_GROUPS(firmware_update);
112 
113 static 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 
120 static 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 
125 static const struct wmi_device_id intel_wmi_sbl_id_table[] = {
126 	{ .guid_string = INTEL_WMI_SBL_GUID },
127 	{}
128 };
129 MODULE_DEVICE_TABLE(wmi, intel_wmi_sbl_id_table);
130 
131 static 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 };
140 module_wmi_driver(intel_wmi_sbl_fw_update_driver);
141 
142 MODULE_AUTHOR("Jithu Joseph <jithu.joseph@intel.com>");
143 MODULE_DESCRIPTION("Slim Bootloader firmware update signaling driver");
144 MODULE_LICENSE("GPL v2");
145