firmware_loader: formalize built-in firmware API

Formalize the built-in firmware with a proper API. This can later
be used by other callers where all they need is built-in firmware.

We export the firmware_request_builtin() call for now only
under the TEST_FIRMWARE symbol namespace as there are no
direct modular users for it. If they pop up they are free
to export it generally. Built-in code always gets access to
the callers and we'll demonstrate a hidden user which has been
lurking in the kernel for a while and the reason why using a
proper API was better long term.

Reviewed-by: Borislav Petkov <[e-mail]>
Signed-off-by: Luis Chamberlain <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/firmware_loader/builtin/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
+obj-y  += main.o
 
 # Create $(fwdir) from $(CONFIG_EXTRA_FIRMWARE_DIR) -- if it doesn't have a
 # leading /, it's relative to $(srctree).
 fwdir := $(subst $(quote),,$(CONFIG_EXTRA_FIRMWARE_DIR))
 fwdir := $(addprefix $(srctree)/,$(filter-out /%,$(fwdir)))$(filter /%,$(fwdir))
 
-obj-y  := $(addsuffix .gen.o, $(subst $(quote),,$(CONFIG_EXTRA_FIRMWARE)))
+firmware  := $(addsuffix .gen.o, $(subst $(quote),,$(CONFIG_EXTRA_FIRMWARE)))
+obj-y += $(firmware)
 
 FWNAME    = $(patsubst $(obj)/%.gen.S,%,$@)
 FWSTR     = $(subst $(comma),_,$(subst /,_,$(subst .,_,$(subst -,_,$(FWNAME)))))
···
 	$(call filechk,fwbin)
 
 # The .o files depend on the binaries directly; the .S files don't.
-$(addprefix $(obj)/, $(obj-y)): $(obj)/%.gen.o: $(fwdir)/%
+$(addprefix $(obj)/, $(firmware)): $(obj)/%.gen.o: $(fwdir)/%
 
 targets := $(patsubst $(obj)/%,%, \
                                 $(shell find $(obj) -name \*.gen.S 2>/dev/null))

drivers/base/firmware_loader/builtin/main.c

···
+// SPDX-License-Identifier: GPL-2.0
+/* Builtin firmware support */
+
+#include <linux/firmware.h>
+#include "../firmware.h"
+
+/* Only if FW_LOADER=y */
+#ifdef CONFIG_FW_LOADER
+
+extern struct builtin_fw __start_builtin_fw[];
+extern struct builtin_fw __end_builtin_fw[];
+
+static bool fw_copy_to_prealloc_buf(struct firmware *fw,
+				    void *buf, size_t size)
+{
+	if (!buf)
+		return true;
+	if (size < fw->size)
+		return false;
+	memcpy(buf, fw->data, fw->size);
+	return true;
+}
+
+/**
+ * firmware_request_builtin() - load builtin firmware
+ * @fw: pointer to firmware struct
+ * @name: name of firmware file
+ *
+ * Some use cases in the kernel have a requirement so that no memory allocator
+ * is involved as these calls take place early in boot process. An example is
+ * the x86 CPU microcode loader. In these cases all the caller wants is to see
+ * if the firmware was built-in and if so use it right away. This can be used
+ * for such cases.
+ *
+ * This looks for the firmware in the built-in kernel. Only if the kernel was
+ * built-in with the firmware you are looking for will this return successfully.
+ *
+ * Callers of this API do not need to use release_firmware() as the pointer to
+ * the firmware is expected to be provided locally on the stack of the caller.
+ **/
+bool firmware_request_builtin(struct firmware *fw, const char *name)
+{
+	struct builtin_fw *b_fw;
+
+	if (!fw)
+		return false;
+
+	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
+		if (strcmp(name, b_fw->name) == 0) {
+			fw->size = b_fw->size;
+			fw->data = b_fw->data;
+			return true;
+		}
+	}
+
+	return false;
+}
+EXPORT_SYMBOL_NS_GPL(firmware_request_builtin, TEST_FIRMWARE);
+
+/**
+ * firmware_request_builtin_buf() - load builtin firmware into optional buffer
+ * @fw: pointer to firmware struct
+ * @name: name of firmware file
+ * @buf: If set this lets you use a pre-allocated buffer so that the built-in
+ *	firmware into is copied into. This field can be NULL. It is used by
+ *	callers such as request_firmware_into_buf() and
+ *	request_partial_firmware_into_buf()
+ * @size: if buf was provided, the max size of the allocated buffer available.
+ *	If the built-in firmware does not fit into the pre-allocated @buf this
+ *	call will fail.
+ *
+ * This looks for the firmware in the built-in kernel. Only if the kernel was
+ * built-in with the firmware you are looking for will this call possibly
+ * succeed. If you passed a @buf the firmware will be copied into it *iff* the
+ * built-in firmware fits into the pre-allocated buffer size specified in
+ * @size.
+ *
+ * This caller is to be used internally by the firmware_loader only.
+ **/
+bool firmware_request_builtin_buf(struct firmware *fw, const char *name,
+				  void *buf, size_t size)
+{
+	if (!firmware_request_builtin(fw, name))
+		return false;
+
+	return fw_copy_to_prealloc_buf(fw, buf, size);
+}
+
+bool firmware_is_builtin(const struct firmware *fw)
+{
+	struct builtin_fw *b_fw;
+
+	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++)
+		if (fw->data == b_fw->data)
+			return true;
+
+	return false;
+}
+
+#endif

drivers/base/firmware_loader/firmware.h

···
 
 int assign_fw(struct firmware *fw, struct device *device);
 
+#ifdef CONFIG_FW_LOADER
+bool firmware_is_builtin(const struct firmware *fw);
+bool firmware_request_builtin_buf(struct firmware *fw, const char *name,
+				  void *buf, size_t size);
+#else /* module case */
+static inline bool firmware_is_builtin(const struct firmware *fw)
+{
+	return false;
+}
+static inline bool firmware_request_builtin_buf(struct firmware *fw,
+						const char *name,
+						void *buf, size_t size)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_FW_LOADER_PAGED_BUF
 void fw_free_paged_buf(struct fw_priv *fw_priv);
 int fw_grow_paged_buf(struct fw_priv *fw_priv, int pages_needed);

drivers/base/firmware_loader/main.c

···
 
 static struct firmware_cache fw_cache;
 
-/* Builtin firmware support */
-
-#ifdef CONFIG_FW_LOADER
-
-extern struct builtin_fw __start_builtin_fw[];
-extern struct builtin_fw __end_builtin_fw[];
-
-static bool fw_copy_to_prealloc_buf(struct firmware *fw,
-				    void *buf, size_t size)
-{
-	if (!buf)
-		return true;
-	if (size < fw->size)
-		return false;
-	memcpy(buf, fw->data, fw->size);
-	return true;
-}
-
-static bool firmware_request_builtin(struct firmware *fw, const char *name)
-{
-	struct builtin_fw *b_fw;
-
-	if (!fw)
-		return false;
-
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++) {
-		if (strcmp(name, b_fw->name) == 0) {
-			fw->size = b_fw->size;
-			fw->data = b_fw->data;
-			return true;
-		}
-	}
-
-	return false;
-}
-
-static bool firmware_request_builtin_buf(struct firmware *fw, const char *name,
-					 void *buf, size_t size)
-{
-	if (!firmware_request_builtin(fw, name))
-		return false;
-	return fw_copy_to_prealloc_buf(fw, buf, size);
-}
-
-static bool fw_is_builtin_firmware(const struct firmware *fw)
-{
-	struct builtin_fw *b_fw;
-
-	for (b_fw = __start_builtin_fw; b_fw != __end_builtin_fw; b_fw++)
-		if (fw->data == b_fw->data)
-			return true;
-
-	return false;
-}
-
-#else /* Module case - no builtin firmware support */
-
-static inline bool firmware_request_builtin(struct firmware *fw,
-					    const char *name)
-{
-	return false;
-}
-
-static inline bool firmware_request_builtin_buf(struct firmware *fw,
-						const char *name, void *buf,
-						size_t size)
-{
-	return false;
-}
-
-static inline bool fw_is_builtin_firmware(const struct firmware *fw)
-{
-	return false;
-}
-#endif
-
 static void fw_state_init(struct fw_priv *fw_priv)
 {
 	struct fw_state *fw_st = &fw_priv->fw_st;
···
 void release_firmware(const struct firmware *fw)
 {
 	if (fw) {
-		if (!fw_is_builtin_firmware(fw))
+		if (!firmware_is_builtin(fw))
 			firmware_free_data(fw);
 		kfree(fw);
 	}

include/linux/firmware.h

···
 struct module;
 struct device;
 
+/*
+ * Built-in firmware functionality is only available if FW_LOADER=y, but not
+ * FW_LOADER=m
+ */
+#ifdef CONFIG_FW_LOADER
 struct builtin_fw {
 	char *name;
 	void *data;
 	unsigned long size;
 };
+
+bool firmware_request_builtin(struct firmware *fw, const char *name);
 
 /* We have to play tricks here much like stringify() to get the
    __COUNTER__ macro to be expanded as we want it */
···
 #define DECLARE_BUILTIN_FIRMWARE_SIZE(name, blob, size)			     \
 	static const struct builtin_fw __fw_concat(__builtin_fw,__COUNTER__) \
 	__used __section(".builtin_fw") = { name, blob, size }
+
+#else
+static inline bool firmware_request_builtin(struct firmware *fw,
+					    const char *name)
+{
+	return false;
+}
+#endif
 
 #if defined(CONFIG_FW_LOADER) || (defined(CONFIG_FW_LOADER_MODULE) && defined(MODULE))
 int request_firmware(const struct firmware **fw, const char *name,