livepatch: introduce shadow variable API

Add exported API for livepatch modules:

  klp_shadow_get()
  klp_shadow_alloc()
  klp_shadow_get_or_alloc()
  klp_shadow_free()
  klp_shadow_free_all()

that implement "shadow" variables, which allow callers to associate new
shadow fields to existing data structures.  This is intended to be used
by livepatch modules seeking to emulate additions to data structure
definitions.

See Documentation/livepatch/shadow-vars.txt for a summary of the new
shadow variable API, including a few common use cases.

See samples/livepatch/livepatch-shadow-* for example modules that
demonstrate shadow variables.

[jkosina@suse.cz: fix __klp_shadow_get_or_alloc() comment as spotted by
 Josh]
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 194991ef9347..d08eddc00497 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -164,6 +164,14 @@ static inline bool klp_have_reliable_stack(void)
 	       IS_ENABLED(CONFIG_HAVE_RELIABLE_STACKTRACE);
 }
 
+void *klp_shadow_get(void *obj, unsigned long id);
+void *klp_shadow_alloc(void *obj, unsigned long id, void *data,
+		       size_t size, gfp_t gfp_flags);
+void *klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
+			      size_t size, gfp_t gfp_flags);
+void klp_shadow_free(void *obj, unsigned long id);
+void klp_shadow_free_all(unsigned long id);
+
 #else /* !CONFIG_LIVEPATCH */
 
 static inline int klp_module_coming(struct module *mod) { return 0; }