On Thu, Oct 12, 2023 at 07:17:19AM +0530, Joey Jiao wrote: > > +config MODULE_DISABLE_INIT_FREE > + bool "Disable freeing of init sections" > + default n > + help > + By default, kernel will free init sections after module being fully > + loaded. > + > + MODULE_DISABLE_INIT_FREE allows users to prevent the freeing of init > + sections. This option is particularly helpful for syzkaller fuzzing, > + ensuring that the module consistently loads into the same address > + across reboots.
How and why does not free'ing init help with syzkaller exactly? I don't see the relationship between not free'ing init and ensuring th emodule loads into the same address. There could be many things which could incur an address gets allocated from a module at another location which a module can take. I cannot fathom how this simple toggle could ensure modules following the address allocations accross reboots. That seems like odd chance, not something actually deterministic. > + > endif # MODULES > diff --git a/kernel/module/main.c b/kernel/module/main.c > index 98fedfdb8db5..0f242b7b29fe 100644 > --- a/kernel/module/main.c > +++ b/kernel/module/main.c > @@ -2593,7 +2593,8 @@ static noinline int do_init_module(struct module *mod) > * be cleaned up needs to sync with the queued work - ie > * rcu_barrier() > */ > - if (llist_add(&freeinit->node, &init_free_list)) > + if (llist_add(&freeinit->node, &init_free_list) && > + !IS_ENABLED(CONFIG_MODULE_DISABLE_INIT_FREE)) > schedule_work(&init_free_wq);
