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
get_fwu_request(struct device * dev,u32 * out)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
set_fwu_request(struct device * dev,u32 in)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
firmware_update_request_show(struct device * dev,struct device_attribute * attr,char * buf)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
firmware_update_request_store(struct device * dev,struct device_attribute * attr,const char * buf,size_t count)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
intel_wmi_sbl_fw_update_probe(struct wmi_device * wdev,const void * context)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
intel_wmi_sbl_fw_update_remove(struct wmi_device * wdev)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
