x86/efi: Implement arch_ima_efi_boot_mode() in source file

The x86 implementation of arch_ima_efi_boot_mode() uses the global
boot_param state. Move it into a source file to clean up the header.
Avoid potential rebuilds of unrelated source files if boot_params
changes.

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20240112095000.8952-4-tzimmermann@suse.de

Author: Thomas Zimmermann

arch/x86/include/asm/efi.h

@@ -409,8 +409,9 @@ extern int __init efi_memmap_split_count(efi_memory_desc_t *md,
 extern void __init efi_memmap_insert(struct efi_memory_map *old_memmap,
 				     void *buf, struct efi_mem_range *mem);
 
-#define arch_ima_efi_boot_mode	\
-	({ extern struct boot_params boot_params; boot_params.secure_boot; })
+extern enum efi_secureboot_mode __x86_ima_efi_boot_mode(void);
+
+#define arch_ima_efi_boot_mode	__x86_ima_efi_boot_mode()
 
 #ifdef CONFIG_EFI_RUNTIME_MAP
 int efi_get_runtime_map_size(void);

arch/x86/platform/efi/efi.c

@@ -950,3 +950,8 @@ umode_t efi_attr_is_visible(struct kobject *kobj, struct attribute *attr, int n)
 	}
 	return attr->mode;
 }
+
+enum efi_secureboot_mode __x86_ima_efi_boot_mode(void)
+{
+	return boot_params.secure_boot;
+}