1 files changed, 247 insertions, 0 deletions
diff --git a/drivers/platform/wmi/marshalling.c b/drivers/platform/wmi/marshalling.c
new file mode 100644
index 000000000000..63a92c4ebab5
--- /dev/null
+++ b/drivers/platform/wmi/marshalling.c
@@ -0,0 +1,247 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * ACPI-WMI buffer marshalling.
+ *
+ * Copyright (C) 2025 Armin Wolf <W_Armin@gmx.de>
+ */
+
+#include <linux/acpi.h>
+#include <linux/align.h>
+#include <linux/math.h>
+#include <linux/overflow.h>
+#include <linux/slab.h>
+#include <linux/unaligned.h>
+#include <linux/wmi.h>
+
+#include <kunit/visibility.h>
+
+#include "internal.h"
+
+static int wmi_adjust_buffer_length(size_t *length, const union acpi_object *obj)
+{
+	size_t alignment, size;
+
+	switch (obj->type) {
+	case ACPI_TYPE_INTEGER:
+		/*
+		 * Integers are threated as 32 bit even if the ACPI DSDT
+		 * declares 64 bit integer width.
+		 */
+		alignment = 4;
+		size = sizeof(u32);
+		break;
+	case ACPI_TYPE_STRING:
+		/*
+		 * Strings begin with a single little-endian 16-bit field containing
+		 * the string length in bytes and are encoded as UTF-16LE with a terminating
+		 * nul character.
+		 */
+		if (obj->string.length + 1 > U16_MAX / 2)
+			return -EOVERFLOW;
+
+		alignment = 2;
+		size = struct_size_t(struct wmi_string, chars, obj->string.length + 1);
+		break;
+	case ACPI_TYPE_BUFFER:
+		/*
+		 * Buffers are copied as-is.
+		 */
+		alignment = 1;
+		size = obj->buffer.length;
+		break;
+	default:
+		return -EPROTO;
+	}
+
+	*length = size_add(ALIGN(*length, alignment), size);
+
+	return 0;
+}
+
+static int wmi_obj_get_buffer_length(const union acpi_object *obj, size_t *length)
+{
+	size_t total = 0;
+	int ret;
+
+	if (obj->type == ACPI_TYPE_PACKAGE) {
+		for (int i = 0; i < obj->package.count; i++) {
+			ret = wmi_adjust_buffer_length(&total, &obj->package.elements[i]);
+			if (ret < 0)
+				return ret;
+		}
+	} else {
+		ret = wmi_adjust_buffer_length(&total, obj);
+		if (ret < 0)
+			return ret;
+	}
+
+	*length = total;
+
+	return 0;
+}
+
+static int wmi_obj_transform_simple(const union acpi_object *obj, u8 *buffer, size_t *consumed)
+{
+	struct wmi_string *string;
+	size_t length;
+	__le32 value;
+	u8 *aligned;
+
+	switch (obj->type) {
+	case ACPI_TYPE_INTEGER:
+		aligned = PTR_ALIGN(buffer, 4);
+		length = sizeof(value);
+
+		value = cpu_to_le32(obj->integer.value);
+		memcpy(aligned, &value, length);
+		break;
+	case ACPI_TYPE_STRING:
+		aligned = PTR_ALIGN(buffer, 2);
+		string = (struct wmi_string *)aligned;
+		length = struct_size(string, chars, obj->string.length + 1);
+
+		/* We do not have to worry about unaligned accesses here as the WMI
+		 * string will already be aligned on a two-byte boundary.
+		 */
+		string->length = cpu_to_le16((obj->string.length + 1) * 2);
+		for (int i = 0; i < obj->string.length; i++)
+			string->chars[i] = cpu_to_le16(obj->string.pointer[i]);
+
+		/*
+		 * The Windows WMI-ACPI driver always emits a terminating nul character,
+		 * so we emulate this behavior here as well.
+		 */
+		string->chars[obj->string.length] = '\0';
+		break;
+	case ACPI_TYPE_BUFFER:
+		aligned = buffer;
+		length = obj->buffer.length;
+
+		memcpy(aligned, obj->buffer.pointer, length);
+		break;
+	default:
+		return -EPROTO;
+	}
+
+	*consumed = (aligned - buffer) + length;
+
+	return 0;
+}
+
+static int wmi_obj_transform(const union acpi_object *obj, u8 *buffer)
+{
+	size_t consumed;
+	int ret;
+
+	if (obj->type == ACPI_TYPE_PACKAGE) {
+		for (int i = 0; i < obj->package.count; i++) {
+			ret = wmi_obj_transform_simple(&obj->package.elements[i], buffer,
+						       &consumed);
+			if (ret < 0)
+				return ret;
+
+			buffer += consumed;
+		}
+	} else {
+		ret = wmi_obj_transform_simple(obj, buffer, &consumed);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
+int wmi_unmarshal_acpi_object(const union acpi_object *obj, struct wmi_buffer *buffer)
+{
+	size_t length, alloc_length;
+	u8 *data;
+	int ret;
+
+	ret = wmi_obj_get_buffer_length(obj, &length);
+	if (ret < 0)
+		return ret;
+
+	if (ARCH_KMALLOC_MINALIGN < 8) {
+		/*
+		 * kmalloc() guarantees that the alignment of the resulting memory allocation is at
+		 * least the largest power-of-two divisor of the allocation size. The WMI buffer
+		 * data needs to be aligned on a 8 byte boundary to properly support 64-bit WMI
+		 * integers, so we have to round the allocation size to the next multiple of 8.
+		 */
+		alloc_length = round_up(length, 8);
+	} else {
+		alloc_length = length;
+	}
+
+	data = kzalloc(alloc_length, GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	ret = wmi_obj_transform(obj, data);
+	if (ret < 0) {
+		kfree(data);
+		return ret;
+	}
+
+	buffer->length = length;
+	buffer->data = data;
+
+	return 0;
+}
+EXPORT_SYMBOL_IF_KUNIT(wmi_unmarshal_acpi_object);
+
+int wmi_marshal_string(const struct wmi_buffer *buffer, struct acpi_buffer *out)
+{
+	const struct wmi_string *string;
+	u16 length, value;
+	size_t chars;
+	char *str;
+
+	if (buffer->length < sizeof(*string))
+		return -ENODATA;
+
+	string = buffer->data;
+	length = get_unaligned_le16(&string->length);
+	if (buffer->length < sizeof(*string) + length)
+		return -ENODATA;
+
+	/* Each character needs to be 16 bits long */
+	if (length % 2)
+		return -EINVAL;
+
+	chars = length / 2;
+	str = kmalloc(chars + 1, GFP_KERNEL);
+	if (!str)
+		return -ENOMEM;
+
+	for (int i = 0; i < chars; i++) {
+		value = get_unaligned_le16(&string->chars[i]);
+
+		/* ACPI only accepts ASCII strings */
+		if (value > 0x7F) {
+			kfree(str);
+			return -EINVAL;
+		}
+
+		str[i] = value & 0xFF;
+
+		/*
+		 * ACPI strings should only contain a single nul character at the end.
+		 * Because of this we must not copy any padding from the WMI string.
+		 */
+		if (!value) {
+			/* ACPICA wants the length of the string without the nul character */
+			out->length = i;
+			out->pointer = str;
+			return 0;
+		}
+	}
+
+	str[chars] = '\0';
+
+	out->length = chars;
+	out->pointer = str;
+
+	return 0;
+}
+EXPORT_SYMBOL_IF_KUNIT(wmi_marshal_string);