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

Josh Poimboeuf
2023-02-04T17:37:36Z

On Thu, Feb 02, 2023 at 11:14:15AM +0100, Petr Mladek wrote:
> 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);
> }
> }

That calls klp_unregister_shadow_types() on the objects for
klp_transition_patch, which is the replacement patch, not the replaced
patch(es).

--
Josh