firmware: Add request_partial_firmware_into_buf()

Add request_partial_firmware_into_buf() to allow for portions of a
firmware file to be read into a buffer. This is needed when large firmware
must be loaded in portions from a file on memory constrained systems.

Signed-off-by: Scott Branden <[e-mail]>
Co-developed-by: Kees Cook <[e-mail]>
Signed-off-by: Kees Cook <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/firmware_loader/firmware.h

···
  * @FW_OPT_FALLBACK_PLATFORM: Enable fallback to device fw copy embedded in
  *	the platform's main firmware. If both this fallback and the sysfs
  *      fallback are enabled, then this fallback will be tried first.
+ * @FW_OPT_PARTIAL: Allow partial read of firmware instead of needing to read
+ *	entire file.
  */
 enum fw_opt {
 	FW_OPT_UEVENT			= BIT(0),
···
 	FW_OPT_NOCACHE			= BIT(4),
 	FW_OPT_NOFALLBACK_SYSFS		= BIT(5),
 	FW_OPT_FALLBACK_PLATFORM	= BIT(6),
+	FW_OPT_PARTIAL			= BIT(7),
 };
 
 enum fw_status {
···
 	void *data;
 	size_t size;
 	size_t allocated_size;
+	size_t offset;
 	u32 opt_flags;
 #ifdef CONFIG_FW_LOADER_PAGED_BUF
 	bool is_paged_buf;

drivers/base/firmware_loader/main.c

···
 					  struct firmware_cache *fwc,
 					  void *dbuf,
 					  size_t size,
+					  size_t offset,
 					  u32 opt_flags)
 {
 	struct fw_priv *fw_priv;
+
+	/* For a partial read, the buffer must be preallocated. */
+	if ((opt_flags & FW_OPT_PARTIAL) && !dbuf)
+		return NULL;
+
+	/* Only partial reads are allowed to use an offset. */
+	if (offset != 0 && !(opt_flags & FW_OPT_PARTIAL))
+		return NULL;
 
 	fw_priv = kzalloc(sizeof(*fw_priv), GFP_ATOMIC);
 	if (!fw_priv)
···
 	fw_priv->fwc = fwc;
 	fw_priv->data = dbuf;
 	fw_priv->allocated_size = size;
+	fw_priv->offset = offset;
 	fw_priv->opt_flags = opt_flags;
 	fw_state_init(fw_priv);
 #ifdef CONFIG_FW_LOADER_USER_HELPER
···
 				struct fw_priv **fw_priv,
 				void *dbuf,
 				size_t size,
+				size_t offset,
 				u32 opt_flags)
 {
 	struct fw_priv *tmp;
 
 	spin_lock(&fwc->lock);
-	if (!(opt_flags & FW_OPT_NOCACHE)) {
+	/*
+	 * Do not merge requests that are marked to be non-cached or
+	 * are performing partial reads.
+	 */
+	if (!(opt_flags & (FW_OPT_NOCACHE | FW_OPT_PARTIAL))) {
 		tmp = __lookup_fw_priv(fw_name);
 		if (tmp) {
 			kref_get(&tmp->ref);
···
 		}
 	}
 
-	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size, opt_flags);
+	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size, offset, opt_flags);
 	if (tmp) {
 		INIT_LIST_HEAD(&tmp->list);
 		if (!(opt_flags & FW_OPT_NOCACHE))
···
 		return -ENOMEM;
 
 	for (i = 0; i < ARRAY_SIZE(fw_path); i++) {
+		size_t file_size = 0;
+		size_t *file_size_ptr = NULL;
+
 		/* skip the unset customized path */
 		if (!fw_path[i][0])
 			continue;
···
 
 		fw_priv->size = 0;
 
+		/*
+		 * The total file size is only examined when doing a partial
+		 * read; the "full read" case needs to fail if the whole
+		 * firmware was not completely loaded.
+		 */
+		if ((fw_priv->opt_flags & FW_OPT_PARTIAL) && buffer)
+			file_size_ptr = &file_size;
+
 		/* load firmware files from the mount namespace of init */
-		rc = kernel_read_file_from_path_initns(path, 0, &buffer, msize,
-						       NULL,
+		rc = kernel_read_file_from_path_initns(path, fw_priv->offset,
+						       &buffer, msize,
+						       file_size_ptr,
 						       READING_FIRMWARE);
 		if (rc < 0) {
 			if (rc != -ENOENT)
···
 static int
 _request_firmware_prepare(struct firmware **firmware_p, const char *name,
 			  struct device *device, void *dbuf, size_t size,
-			  u32 opt_flags)
+			  size_t offset, u32 opt_flags)
 {
 	struct firmware *firmware;
 	struct fw_priv *fw_priv;
···
 	}
 
 	ret = alloc_lookup_fw_priv(name, &fw_cache, &fw_priv, dbuf, size,
-				  opt_flags);
+				   offset, opt_flags);
 
 	/*
 	 * bind with 'priv' now to avoid warning in failure path
···
 static int
 _request_firmware(const struct firmware **firmware_p, const char *name,
 		  struct device *device, void *buf, size_t size,
-		  u32 opt_flags)
+		  size_t offset, u32 opt_flags)
 {
 	struct firmware *fw = NULL;
+	bool nondirect = false;
 	int ret;
 
 	if (!firmware_p)
···
 	}
 
 	ret = _request_firmware_prepare(&fw, name, device, buf, size,
-					opt_flags);
+					offset, opt_flags);
 	if (ret <= 0) /* error or already assigned */
 		goto out;
 
 	ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL);
+
+	/* Only full reads can support decompression, platform, and sysfs. */
+	if (!(opt_flags & FW_OPT_PARTIAL))
+		nondirect = true;
+
 #ifdef CONFIG_FW_LOADER_COMPRESS
-	if (ret == -ENOENT)
+	if (ret == -ENOENT && nondirect)
 		ret = fw_get_filesystem_firmware(device, fw->priv, ".xz",
 						 fw_decompress_xz);
 #endif
-
-	if (ret == -ENOENT)
+	if (ret == -ENOENT && nondirect)
 		ret = firmware_fallback_platform(fw->priv);
 
 	if (ret) {
···
 			dev_warn(device,
 				 "Direct firmware load for %s failed with error %d\n",
 				 name, ret);
-		ret = firmware_fallback_sysfs(fw, name, device, opt_flags, ret);
+		if (nondirect)
+			ret = firmware_fallback_sysfs(fw, name, device,
+						      opt_flags, ret);
 	} else
 		ret = assign_fw(fw, device);
 
···
 
 	/* Need to pin this module until return */
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware_p, name, device, NULL, 0,
+	ret = _request_firmware(firmware_p, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT);
 	module_put(THIS_MODULE);
 	return ret;
···
 
 	/* Need to pin this module until return */
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware, name, device, NULL, 0,
+	ret = _request_firmware(firmware, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT | FW_OPT_NO_WARN);
 	module_put(THIS_MODULE);
 	return ret;
···
 	int ret;
 
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware_p, name, device, NULL, 0,
+	ret = _request_firmware(firmware_p, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT | FW_OPT_NO_WARN |
 				FW_OPT_NOFALLBACK_SYSFS);
 	module_put(THIS_MODULE);
···
 
 	/* Need to pin this module until return */
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware, name, device, NULL, 0,
+	ret = _request_firmware(firmware, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT | FW_OPT_FALLBACK_PLATFORM);
 	module_put(THIS_MODULE);
 	return ret;
···
 		return -EOPNOTSUPP;
 
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware_p, name, device, buf, size,
+	ret = _request_firmware(firmware_p, name, device, buf, size, 0,
 				FW_OPT_UEVENT | FW_OPT_NOCACHE);
 	module_put(THIS_MODULE);
 	return ret;
 }
 EXPORT_SYMBOL(request_firmware_into_buf);
+
+/**
+ * request_partial_firmware_into_buf() - load partial firmware into a previously allocated buffer
+ * @firmware_p: pointer to firmware image
+ * @name: name of firmware file
+ * @device: device for which firmware is being loaded and DMA region allocated
+ * @buf: address of buffer to load firmware into
+ * @size: size of buffer
+ * @offset: offset into file to read
+ *
+ * This function works pretty much like request_firmware_into_buf except
+ * it allows a partial read of the file.
+ */
+int
+request_partial_firmware_into_buf(const struct firmware **firmware_p,
+				  const char *name, struct device *device,
+				  void *buf, size_t size, size_t offset)
+{
+	int ret;
+
+	if (fw_cache_is_setup(device, name))
+		return -EOPNOTSUPP;
+
+	__module_get(THIS_MODULE);
+	ret = _request_firmware(firmware_p, name, device, buf, size, offset,
+				FW_OPT_UEVENT | FW_OPT_NOCACHE |
+				FW_OPT_PARTIAL);
+	module_put(THIS_MODULE);
+	return ret;
+}
+EXPORT_SYMBOL(request_partial_firmware_into_buf);
 
 /**
  * release_firmware() - release the resource associated with a firmware image
···
 
 	fw_work = container_of(work, struct firmware_work, work);
 
-	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0,
+	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0, 0,
 			  fw_work->opt_flags);
 	fw_work->cont(fw, fw_work->context);
 	put_device(fw_work->device); /* taken in request_firmware_nowait() */

include/linux/firmware.h

···
 			    struct device *device);
 int request_firmware_into_buf(const struct firmware **firmware_p,
 	const char *name, struct device *device, void *buf, size_t size);
+int request_partial_firmware_into_buf(const struct firmware **firmware_p,
+				      const char *name, struct device *device,
+				      void *buf, size_t size, size_t offset);
 
 void release_firmware(const struct firmware *fw);
 #else
···
 
 static inline int request_firmware_into_buf(const struct firmware **firmware_p,
 	const char *name, struct device *device, void *buf, size_t size)
+{
+	return -EINVAL;
+}
+
+static inline int request_partial_firmware_into_buf
+					(const struct firmware **firmware_p,
+					 const char *name,
+					 struct device *device,
+					 void *buf, size_t size, size_t offset)
 {
 	return -EINVAL;
 }