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// SPDX-License-Identifier: GPL-2.0
/*
* Slim Bootloader(SBL) firmware update signaling driver
*
* Slim Bootloader is a small, open-source, non UEFI compliant, boot firmware
* optimized for running on certain Intel platforms.
*
* SBL exposes an ACPI-WMI device via /sys/bus/wmi/devices/<INTEL_WMI_SBL_GUID>.
* This driver further adds "firmware_update_request" device attribute.
* This attribute normally has a value of 0 and userspace can signal SBL
* to update firmware, on next reboot, by writing a value of 1.
*
* More details of SBL firmware update process is available at:
* https://slimbootloader.github.io/security/firmware-update.html
*/
#include <linux/acpi.h>
#include <linux/device.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/sysfs.h>
#include <linux/wmi.h>
#define INTEL_WMI_SBL_GUID "44FADEB1-B204-40F2-8581-394BBDC1B651"
static int get_fwu_request(struct device *dev, u32 *out)
{
union acpi_object *obj;
obj = wmidev_block_query(to_wmi_device(dev), 0);
if (!obj)
return -ENODEV;
if (obj->type != ACPI_TYPE_INTEGER) {
dev_warn(dev, "wmi_query_block returned invalid value\n");
kfree(obj);
return -EINVAL;
}
*out = obj->integer.value;
kfree(obj);
return 0;
}
static int set_fwu_request(struct device *dev, u32 in)
{
struct acpi_buffer input;
acpi_status status;
u32 value;
value = in;
input.length = sizeof(u32);
input.pointer = &value;
status = wmidev_block_set(to_wmi_device(dev), 0, &input);
if (ACPI_FAILURE(status)) {
dev_err(dev, "wmi_set_block failed\n");
return -ENODEV;
}
return 0;
}
static ssize_t firmware_update_request_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
u32 val;
int ret;
ret = get_fwu_request(dev, &val);
if (ret)
return ret;
return sprintf(buf, "%d\n", val);
}
static ssize_t firmware_update_request_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
unsigned int val;
int ret;
ret = kstrtouint(buf, 0, &val);
if (ret)
return ret;
/* May later be extended to support values other than 0 and 1 */
if (val > 1)
return -ERANGE;
ret = set_fwu_request(dev, val);
if (ret)
return ret;
return count;
}
static DEVICE_ATTR_RW(firmware_update_request);
static struct attribute *firmware_update_attrs[] = {
&dev_attr_firmware_update_request.attr,
NULL
};
ATTRIBUTE_GROUPS(firmware_update);
static int intel_wmi_sbl_fw_update_probe(struct wmi_device *wdev,
const void *context)
{
dev_info(&wdev->dev, "Slim Bootloader signaling driver attached\n");
return 0;
}
static void intel_wmi_sbl_fw_update_remove(struct wmi_device *wdev)
{
dev_info(&wdev->dev, "Slim Bootloader signaling driver removed\n");
}
static const struct wmi_device_id intel_wmi_sbl_id_table[] = {
{ .guid_string = INTEL_WMI_SBL_GUID },
{}
};
MODULE_DEVICE_TABLE(wmi, intel_wmi_sbl_id_table);
static struct wmi_driver intel_wmi_sbl_fw_update_driver = {
.driver = {
.name = "intel-wmi-sbl-fw-update",
.dev_groups = firmware_update_groups,
},
.probe = intel_wmi_sbl_fw_update_probe,
.remove = intel_wmi_sbl_fw_update_remove,
.id_table = intel_wmi_sbl_id_table,
};
module_wmi_driver(intel_wmi_sbl_fw_update_driver);
MODULE_AUTHOR("Jithu Joseph <jithu.joseph@intel.com>");
MODULE_DESCRIPTION("Slim Bootloader firmware update signaling driver");
MODULE_LICENSE("GPL v2");
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