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>
---
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;
+
+ *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)) }
--
2.52.0On 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@suse.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@redhat.com>
--
Joe
On 1/19/26 11:19 PM, Joe Lawrence wrote:
> 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@suse.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 :)
Makes sense. I'll change the function signature to:
void *klp_locate_section_objs(const struct module *mod, const char *name, size_t object_size, unsigned int *nr_objs);
--
Thanks,
Petr
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