hwmon: (hp-wmi-sensors) Fix failure to load on EliteDesk 800 G6

The EliteDesk 800 G6 stores a raw WMI string within the ACPI object in its
BIOS corresponding to one instance of HPBIOS_PlatformEvents.Name. This is
evidently a valid way of representing a WMI data item as far as the
Microsoft ACPI-WMI mapper is concerned, but is preventing the driver from
loading.

This seems quite rare, but add support for such strings. Treating this as a
quirk pretty much means adding that support anyway.

Also clean up an oversight in update_numeric_sensor_from_wobj() in which
the result of hp_wmi_strdup() was being used without error checking.

Reported-by: Lukasz Stelmach <[e-mail]>
Closes: https://lore.kernel.org/linux-hwmon/[e-mail]/
Tested-by: Lukasz Stelmach <[e-mail]>
Signed-off-by: James Seo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Guenter Roeck <[e-mail]>

drivers/hwmon/hp-wmi-sensors.c

···
  *     Available: https://github.com/linuxhw/ACPI
  * [4] P. Rohár, "bmfdec - Decompile binary MOF file (BMF) from WMI buffer",
  *     2017. [Online]. Available: https://github.com/pali/bmfdec
+ * [5] Microsoft Corporation, "Driver-Defined WMI Data Items", 2017. [Online].
+ *     Available: https://learn.microsoft.com/en-us/windows-hardware/drivers/kernel/driver-defined-wmi-data-items
  */
 
 #include <linux/acpi.h>
···
 #include <linux/hwmon.h>
 #include <linux/jiffies.h>
 #include <linux/mutex.h>
+#include <linux/nls.h>
 #include <linux/units.h>
 #include <linux/wmi.h>
 
···
 	struct mutex lock;	/* Lock polling WMI and driver state changes. */
 };
 
+static bool is_raw_wmi_string(const u8 *pointer, u32 length)
+{
+	const u16 *ptr;
+	u16 len;
+
+	/* WMI strings are length-prefixed UTF-16 [5]. */
+	if (length <= sizeof(*ptr))
+		return false;
+
+	length -= sizeof(*ptr);
+	ptr = (const u16 *)pointer;
+	len = *ptr;
+
+	return len <= length && !(len & 1);
+}
+
+static char *convert_raw_wmi_string(const u8 *buf)
+{
+	const wchar_t *src;
+	unsigned int cps;
+	unsigned int len;
+	char *dst;
+	int i;
+
+	src = (const wchar_t *)buf;
+
+	/* Count UTF-16 code points. Exclude trailing null padding. */
+	cps = *src / sizeof(*src);
+	while (cps && !src[cps])
+		cps--;
+
+	/* Each code point becomes up to 3 UTF-8 characters. */
+	len = min(cps * 3, HP_WMI_MAX_STR_SIZE - 1);
+
+	dst = kmalloc((len + 1) * sizeof(*dst), GFP_KERNEL);
+	if (!dst)
+		return NULL;
+
+	i = utf16s_to_utf8s(++src, cps, UTF16_LITTLE_ENDIAN, dst, len);
+	dst[i] = '\0';
+
+	return dst;
+}
+
 /* hp_wmi_strdup - devm_kstrdup, but length-limited */
 static char *hp_wmi_strdup(struct device *dev, const char *src)
 {
···
 		return NULL;
 
 	strscpy(dst, src, len + 1);
+
+	return dst;
+}
+
+/* hp_wmi_wstrdup - hp_wmi_strdup, but for a raw WMI string */
+static char *hp_wmi_wstrdup(struct device *dev, const u8 *buf)
+{
+	char *src;
+	char *dst;
+
+	src = convert_raw_wmi_string(buf);
+	if (!src)
+		return NULL;
+
+	dst = hp_wmi_strdup(dev, strim(src));	/* Note: Copy is trimmed. */
+
+	kfree(src);
 
 	return dst;
 }
···
 	for (prop = 0; prop <= last_prop; prop++) {
 		type = elements[prop].type;
 		valid_type = property_map[prop];
-		if (type != valid_type)
+		if (type != valid_type) {
+			if (type == ACPI_TYPE_BUFFER &&
+			    valid_type == ACPI_TYPE_STRING &&
+			    is_raw_wmi_string(elements[prop].buffer.pointer,
+					      elements[prop].buffer.length))
+				continue;
 			return -EINVAL;
+		}
 	}
 
 	return 0;
···
 		break;
 
 	case ACPI_TYPE_STRING:
-		*out_string = hp_wmi_strdup(dev, strim(element->string.pointer));
+		*out_string = element->type == ACPI_TYPE_BUFFER ?
+			hp_wmi_wstrdup(dev, element->buffer.pointer) :
+			hp_wmi_strdup(dev, strim(element->string.pointer));
 		if (!*out_string)
 			return -ENOMEM;
 		break;
···
 {
 	const union acpi_object *elements;
 	const union acpi_object *element;
-	const char *string;
+	const char *new_string;
+	char *trimmed;
+	char *string;
 	bool is_new;
 	int offset;
 	u8 size;
···
 	offset = is_new ? size - 1 : -2;
 
 	element = &elements[HP_WMI_PROPERTY_CURRENT_STATE + offset];
-	string = strim(element->string.pointer);
+	string = element->type == ACPI_TYPE_BUFFER ?
+		convert_raw_wmi_string(element->buffer.pointer) :
+		element->string.pointer;
 
-	if (strcmp(string, nsensor->current_state)) {
-		devm_kfree(dev, nsensor->current_state);
-		nsensor->current_state = hp_wmi_strdup(dev, string);
+	if (string) {
+		trimmed = strim(string);
+		if (strcmp(trimmed, nsensor->current_state)) {
+			new_string = hp_wmi_strdup(dev, trimmed);
+			if (new_string) {
+				devm_kfree(dev, nsensor->current_state);
+				nsensor->current_state = new_string;
+			}
+		}
+		if (element->type == ACPI_TYPE_BUFFER)
+			kfree(string);
 	}
 
 	/* Old variant: -2 (not -1) because it lacks the Size property. */
···
 			  HP_WMI_EVENT_PROPERTY_STATUS);
 }
 
-static int populate_event_from_wobj(struct hp_wmi_event *event,
+static int populate_event_from_wobj(struct device *dev,
+				    struct hp_wmi_event *event,
 				    union acpi_object *wobj)
 {
 	int prop = HP_WMI_EVENT_PROPERTY_NAME;
 	union acpi_object *element;
+	acpi_object_type type;
+	char *string;
+	u32 value;
 	int err;
 
 	err = check_event_wobj(wobj);
···
 
 	element = wobj->package.elements;
 
-	/* Extracted strings are NOT device-managed copies. */
-
 	for (; prop <= HP_WMI_EVENT_PROPERTY_CATEGORY; prop++, element++) {
+		type = hp_wmi_event_property_map[prop];
+
+		err = extract_acpi_value(dev, element, type, &value, &string);
+		if (err)
+			return err;
+
 		switch (prop) {
 		case HP_WMI_EVENT_PROPERTY_NAME:
-			event->name = strim(element->string.pointer);
+			event->name = string;
 			break;
 
 		case HP_WMI_EVENT_PROPERTY_DESCRIPTION:
-			event->description = strim(element->string.pointer);
+			event->description = string;
 			break;
 
 		case HP_WMI_EVENT_PROPERTY_CATEGORY:
-			event->category = element->integer.value;
+			event->category = value;
 			break;
 
 		default:
···
 	struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
 	struct hp_wmi_sensors *state = context;
 	struct device *dev = &state->wdev->dev;
+	struct hp_wmi_event event = {};
 	struct hp_wmi_info *fan_info;
-	struct hp_wmi_event event;
 	union acpi_object *wobj;
 	acpi_status err;
 	int event_type;
···
 
 	wobj = out.pointer;
 
-	err = populate_event_from_wobj(&event, wobj);
+	err = populate_event_from_wobj(dev, &event, wobj);
 	if (err) {
 		dev_warn(dev, "Bad event data (ACPI type %d)\n", wobj->type);
 		goto out_free_wobj;
···
 
 out_free_wobj:
 	kfree(wobj);
+
+	devm_kfree(dev, event.name);
+	devm_kfree(dev, event.description);
 
 out_unlock:
 	mutex_unlock(&state->lock);