Commit ab108154 authored by Petr Pavlu's avatar Petr Pavlu Committed by Josh Poimboeuf
Browse files

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: dd590d4d ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Signed-off-by: default avatarPetr Pavlu <petr.pavlu@suse.com>
Acked-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Acked-by: default avatarMiroslav Benes <mbenes@suse.cz>
Reviewed-by: default avatarAaron Tomlin <atomlin@atomlin.com>
Link: https://patch.msgid.link/20260123102825.3521961-2-petr.pavlu@suse.com


Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
parent a8ff29f0

include/linux/livepatch.h

+3 −0
Original line number Diff line number Diff line
@@ -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_find_section_by_name(const struct module *mod, const char *name,

			       size_t *sec_size);



void klp_copy_process(struct task_struct *child);

void klp_update_patch_state(struct task_struct *task);

kernel/livepatch/core.c

+19 −0
Original line number Diff line number Diff line
@@ -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);

scripts/livepatch/init.c

+9 −11
Original line number Diff line number Diff line
@@ -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 @@ 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);

scripts/module.lds.S

+1 −6
Original line number Diff line number Diff line
@@ -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)) }