Re: [PATCH v2 4/4] livepatch/shadow: Add garbage collection of shadow variables

Petr Mladek
2023-02-02T10:14:20Z

On Tue 2023-01-31 16:18:17, Josh Poimboeuf wrote:
> On Wed, Oct 26, 2022 at 04:41:22PM -0300, Marcos Paulo de Souza wrote:
> > The shadow variable type might then be added into a new @shadow_types
> > member of struct klp_object. They will get then automatically registered
> > and unregistered when the object is being livepatched. The registration
> > increments the reference count. Unregistration decreases the reference
> > count. All shadow variables of the given type are freed when the reference
> > count reaches zero.
>
> How does the automatic unregistration work for replaced patches?
>
> I see klp_unpatch_replaced_patches() is called, but I don't see where it
> ends up calling klp_shadow_unregister() for the replaced patch(es).

Great catch! I forgot that replaced patches are handled separately.
We should do the following (on top of this patch):

--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -123,8 +123,11 @@ static void klp_complete_transition(void)
continue;
if (klp_target_state == KLP_PATCHED)
klp_post_patch_callback(obj);
- else if (klp_target_state == KLP_UNPATCHED) {
+ else if (klp_target_state == KLP_UNPATCHED)
klp_post_unpatch_callback(obj);
+
+ if (klp_target_state == KLP_UNPATCHED ||
+ klp_transition_patch->replace) {
klp_unregister_shadow_types(obj);
}
}

Also we should add more selftests for handling the shadow variables.

Best Regards,
Petr