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 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
set_fwu_request(struct device * dev,u32 in)46 static 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
firmware_update_request_show(struct device * dev,struct device_attribute * attr,char * buf)65 static 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
firmware_update_request_store(struct device * dev,struct device_attribute * attr,const char * buf,size_t count)79 static 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 }
100 static DEVICE_ATTR_RW(firmware_update_request);
101
102 static struct attribute *firmware_update_attrs[] = {
103 &dev_attr_firmware_update_request.attr,
104 NULL
105 };
106 ATTRIBUTE_GROUPS(firmware_update);
107
intel_wmi_sbl_fw_update_probe(struct wmi_device * wdev,const void * context)108 static 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
intel_wmi_sbl_fw_update_remove(struct wmi_device * wdev)115 static 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
120 static const struct wmi_device_id intel_wmi_sbl_id_table[] = {
121 { .guid_string = INTEL_WMI_SBL_GUID },
122 {}
123 };
124 MODULE_DEVICE_TABLE(wmi, intel_wmi_sbl_id_table);
125
126 static 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 };
136 module_wmi_driver(intel_wmi_sbl_fw_update_driver);
137
138 MODULE_AUTHOR("Jithu Joseph <jithu.joseph@intel.com>");
139 MODULE_DESCRIPTION("Slim Bootloader firmware update signaling driver");
140 MODULE_LICENSE("GPL v2");
141