[PATCH v2 1/2] livepatch: Fix having __klp_objects relics in non-livepatch modules

[Petr Pavlu <petr.pavlu@suse.com>]

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.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
---
 include/linux/livepatch.h |  3 +++
 kernel/livepatch/core.c   | 20 ++++++++++++++++++++
 scripts/livepatch/init.c  | 18 +++++++-----------
 scripts/module.lds.S      |  7 +------
 4 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 772919e8096a..0a663e5911f4 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -175,6 +175,9 @@ int klp_enable_patch(struct klp_patch *);
 int klp_module_coming(struct module *mod);
 void klp_module_going(struct module *mod);
 
+void *klp_locate_section_objs(const struct module *mod, const char *name,
+			      size_t object_size, unsigned int *nr_objs);
+
 void klp_copy_process(struct task_struct *child);
 void klp_update_patch_state(struct task_struct *task);
 
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 9917756dae46..85925abfca0f 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -1356,6 +1356,26 @@ void klp_module_going(struct module *mod)
 	mutex_unlock(&klp_mutex);
 }
 
+void *klp_locate_section_objs(const struct module *mod, const char *name,
+			      size_t object_size, unsigned int *nr_objs)
+{
+	struct klp_modinfo *info = mod->klp_info;
+
+	for (int i = 1; i < info->hdr.e_shnum; i++) {
+		Elf_Shdr *shdr = &info->sechdrs[i];
+
+		if (strcmp(info->secstrings + shdr->sh_name, name))
+			continue;
+
+		*nr_objs = shdr->sh_size / object_size;
+		return (void *)shdr->sh_addr;
+	}
+
+	*nr_objs = 0;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(klp_locate_section_objs);
+
 static int __init klp_init(void)
 {
 	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
diff --git a/scripts/livepatch/init.c b/scripts/livepatch/init.c
index 2274d8f5a482..a02252e1de03 100644
--- a/scripts/livepatch/init.c
+++ b/scripts/livepatch/init.c
@@ -9,19 +9,17 @@
 #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;
 	struct klp_object *objs;
 	unsigned int nr_objs;
 	int ret;
 
-	nr_objs = __stop_klp_objects - __start_klp_objects;
-
+	obj_exts = klp_locate_section_objs(THIS_MODULE, "__klp_objects",
+					   sizeof(*obj_exts), &nr_objs);
 	if (!nr_objs) {
 		pr_err("nothing to patch!\n");
 		ret = -EINVAL;
@@ -41,7 +39,7 @@ 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 +88,10 @@ static int __init livepatch_mod_init(void)
 
 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)) }
-- 
2.52.0