livepatch: Fix having __klp_objects relics in non-livepatch modules

The linker script scripts/module.lds.S specifies that all input
__klp_objects sections should be consolidated into an output section of
the same name, and start/stop symbols should be created to enable
scripts/livepatch/init.c to locate this data.

This start/stop pattern is not ideal for modules because the symbols are
created even if no __klp_objects input sections are present.
Consequently, a dummy __klp_objects section also appears in the
resulting module. This unnecessarily pollutes non-livepatch modules.

Instead, since modules are relocatable files, the usual method for
locating consolidated data in a module is to read its section table.
This approach avoids the aforementioned problem.

The klp_modinfo already stores a copy of the entire section table with
the final addresses. Introduce a helper function that
scripts/livepatch/init.c can call to obtain the location of the
__klp_objects section from this data.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Link: https://patch.msgid.link/20260123102825.3521961-2-petr.pavlu@suse.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

2 files changed, 10 insertions, 17 deletions

diff --git a/scripts/livepatch/init.c b/scripts/livepatch/init.c
index 2274d8f5a482..9e315fc857bd 100644
--- a/scripts/livepatch/init.c
+++ b/scripts/livepatch/init.c
@@ -9,19 +9,19 @@
 #include <linux/slab.h>
 #include <linux/livepatch.h>
 
-extern struct klp_object_ext __start_klp_objects[];
-extern struct klp_object_ext __stop_klp_objects[];
-
 static struct klp_patch *patch;
 
 static int __init livepatch_mod_init(void)
 {
+	struct klp_object_ext *obj_exts;
+	size_t obj_exts_sec_size;
 	struct klp_object *objs;
 	unsigned int nr_objs;
 	int ret;
 
-	nr_objs = __stop_klp_objects - __start_klp_objects;
-
+	obj_exts = klp_find_section_by_name(THIS_MODULE, "__klp_objects",
+					    &obj_exts_sec_size);
+	nr_objs = obj_exts_sec_size / sizeof(*obj_exts);
 	if (!nr_objs) {
 		pr_err("nothing to patch!\n");
 		ret = -EINVAL;
@@ -41,7 +41,7 @@ static int __init livepatch_mod_init(void)
 	}
 
 	for (int i = 0; i < nr_objs; i++) {
-		struct klp_object_ext *obj_ext = __start_klp_objects + i;
+		struct klp_object_ext *obj_ext = obj_exts + i;
 		struct klp_func_ext *funcs_ext = obj_ext->funcs;
 		unsigned int nr_funcs = obj_ext->nr_funcs;
 		struct klp_func *funcs = objs[i].funcs;
@@ -90,12 +90,10 @@ err:
 
 static void __exit livepatch_mod_exit(void)
 {
-	unsigned int nr_objs;
-
-	nr_objs = __stop_klp_objects - __start_klp_objects;
+	struct klp_object *obj;
 
-	for (int i = 0; i < nr_objs; i++)
-		kfree(patch->objs[i].funcs);
+	klp_for_each_object_static(patch, obj)
+		kfree(obj->funcs);
 
 	kfree(patch->objs);
 	kfree(patch);
diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 3037d5e5527c..383d19beffb4 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -35,12 +35,7 @@ SECTIONS {
 	__patchable_function_entries : { *(__patchable_function_entries) }
 
 	__klp_funcs		0: ALIGN(8) { KEEP(*(__klp_funcs)) }
-
-	__klp_objects		0: ALIGN(8) {
-		__start_klp_objects = .;
-		KEEP(*(__klp_objects))
-		__stop_klp_objects = .;
-	}
+	__klp_objects		0: ALIGN(8) { KEEP(*(__klp_objects)) }
 
 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
 	__kcfi_traps		: { KEEP(*(.kcfi_traps)) }