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>

1 files changed, 19 insertions, 0 deletions

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 9917756dae46..1acbad2dbfdf 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -1356,6 +1356,25 @@ void klp_module_going(struct module *mod)
 	mutex_unlock(&klp_mutex);
 }
 
+void *klp_find_section_by_name(const struct module *mod, const char *name,
+			       size_t *sec_size)
+{
+	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)) {
+			*sec_size = shdr->sh_size;
+			return (void *)shdr->sh_addr;
+		}
+	}
+
+	*sec_size = 0;
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(klp_find_section_by_name);
+
 static int __init klp_init(void)
 {
 	klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);