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Message-ID: <aW6uCQNXj0Y7IGnz@redhat.com>
Date: Mon, 19 Jan 2026 17:19:53 -0500
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Petr Pavlu <petr.pavlu@...e.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, Jiri Kosina <jikos@...nel.org>,
Miroslav Benes <mbenes@...e.cz>, Petr Mladek <pmladek@...e.com>,
Luis Chamberlain <mcgrof@...nel.org>,
Daniel Gomez <da.gomez@...nel.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
Aaron Tomlin <atomlin@...mlin.com>,
Peter Zijlstra <peterz@...radead.org>,
live-patching@...r.kernel.org, linux-modules@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] livepatch: Fix having __klp_objects relics in
non-livepatch modules
On Wed, Jan 14, 2026 at 01:29:53PM +0100, Petr Pavlu wrote:
> 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@...e.com>
> ---
> include/linux/livepatch.h | 3 +++
> kernel/livepatch/core.c | 20 ++++++++++++++++++++
> scripts/livepatch/init.c | 17 ++++++-----------
> scripts/module.lds.S | 7 +------
> 4 files changed, 30 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
> index 772919e8096a..ca90adbe89ed 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);
>
> +struct klp_object_ext *klp_build_locate_init_objects(const struct module *mod,
> + 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..4e0ac47b3623 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);
> }
>
> +struct klp_object_ext *klp_build_locate_init_objects(const struct module *mod,
> + 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, "__klp_objects"))
> + continue;
> +
Since this function is doing a string comparision to find the ELF
section, would it make sense to open up the API by allowing to caller to
specify the sh_name? That would give scripts/livepatch/init.c future
flexibility in finding similarly crafted data structures. Disregard if
there is already a pattern of doing it this way :)
> + *nr_objs = shdr->sh_size / sizeof(struct klp_object_ext);
> + return (struct klp_object_ext *)shdr->sh_addr;
> + }
> +
> + *nr_objs = 0;
> + return NULL;
> +}
> +EXPORT_SYMBOL_GPL(klp_build_locate_init_objects);
> +
> 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..23e037d6de19 100644
> --- a/scripts/livepatch/init.c
> +++ b/scripts/livepatch/init.c
> @@ -9,19 +9,16 @@
> #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_build_locate_init_objects(THIS_MODULE, &nr_objs);
> if (!nr_objs) {
> pr_err("nothing to patch!\n");
> ret = -EINVAL;
> @@ -41,7 +38,7 @@ 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 +87,10 @@ 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
>
Acked-by: Joe Lawrence <joe.lawrence@...hat.com>
--
Joe
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