arm64/efi: efistub: Apply __init annotation

This ensures all stub component are freed when the kernel proper is
done booting, by prefixing the names of all ELF sections that have
the SHF_ALLOC attribute with ".init". This approach ensures that even
implicitly emitted allocated data (like initializer values and string
literals) are covered.

At the same time, remove some __init annotations in the stub that have
now become redundant, and add the __init annotation to handle_kernel_image
which will now trigger a section mismatch warning without it.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

arch/arm64/kernel/efi-stub.c

@@ -13,7 +13,7 @@
 #include <asm/efi.h>
 #include <asm/sections.h>
 
-efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
+efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table,
 					unsigned long *image_addr,
 					unsigned long *image_size,
 					unsigned long *reserve_addr,

drivers/firmware/efi/libstub/Makefile

@@ -24,3 +24,17 @@ lib-y				:= efi-stub-helper.o
 lib-$(CONFIG_EFI_ARMSTUB)	+= arm-stub.o fdt.o
 
 CFLAGS_fdt.o			+= -I$(srctree)/scripts/dtc/libfdt/
+
+#
+# arm64 puts the stub in the kernel proper, which will unnecessarily retain all
+# code indefinitely unless it is annotated as __init/__initdata/__initconst etc.
+# So let's apply the __init annotations at the section level, by prefixing
+# the section names directly. This will ensure that even all the inline string
+# literals are covered.
+#
+extra-$(CONFIG_ARM64)		:= $(lib-y)
+lib-$(CONFIG_ARM64)		:= $(patsubst %.o,%.init.o,$(lib-y))
+
+OBJCOPYFLAGS := --prefix-alloc-sections=.init
+$(obj)/%.init.o: $(obj)/%.o FORCE
+	$(call if_changed,objcopy)

drivers/firmware/efi/libstub/arm-stub.c

@@ -17,10 +17,10 @@
 
 #include "efistub.h"
 
-static int __init efi_secureboot_enabled(efi_system_table_t *sys_table_arg)
+static int efi_secureboot_enabled(efi_system_table_t *sys_table_arg)
 {
-	static efi_guid_t const var_guid __initconst = EFI_GLOBAL_VARIABLE_GUID;
-	static efi_char16_t const var_name[] __initconst = {
+	static efi_guid_t const var_guid = EFI_GLOBAL_VARIABLE_GUID;
+	static efi_char16_t const var_name[] = {
 		'S', 'e', 'c', 'u', 'r', 'e', 'B', 'o', 'o', 't', 0 };
 
 	efi_get_variable_t *f_getvar = sys_table_arg->runtime->get_variable;
@@ -164,7 +164,7 @@ efi_status_t handle_kernel_image(efi_system_table_t *sys_table,
  * for both archictectures, with the arch-specific code provided in the
  * handle_kernel_image() function.
  */
-unsigned long __init efi_entry(void *handle, efi_system_table_t *sys_table,
+unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
 			       unsigned long *image_addr)
 {
 	efi_loaded_image_t *image;

drivers/firmware/efi/libstub/efi-stub-helper.c

@@ -101,7 +101,7 @@ efi_status_t efi_get_memory_map(efi_system_table_t *sys_table_arg,
 }
 
 
-unsigned long __init get_dram_base(efi_system_table_t *sys_table_arg)
+unsigned long get_dram_base(efi_system_table_t *sys_table_arg)
 {
 	efi_status_t status;
 	unsigned long map_size;