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");