Re: [PATCH] sched: fix build with GCC_PLUGIN_RANDSTRUCT

[Mike Rapoport]

On Sat, Jun 27, 2020 at 06:12:14PM -0400, Steven Rostedt wrote:
> On Sat, 20 Jun 2020 13:41:36 +0300
> Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> 
> > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > 
> > Since the commit a148866489fb ("sched: Replace rq::wake_list")
> > task_struct and CSD_TYPE_TTWU objects can be on the same queue and this
> > requires that have "layout similar enough".
> > 
> > This assumption is broken when CONFIG_GCC_PLUGIN_RANDSTRUCT is enabled:
> 
> You forgot to Cc Kees, who's the one that is probably the most
> concerned about randomizing structures!

I was not concerned about randomizing, I was troubled by failing
allyesconfig builds :)

> >  	/*
> >  	 * This begins the randomizable portion of task_struct. Only
> >  	 * scheduling-critical items should be added above here.
> > @@ -654,8 +663,6 @@ struct task_struct {
> >  	unsigned int			ptrace;
> >  
> >  #ifdef CONFIG_SMP
> > -	struct llist_node		wake_entry;
> > -	unsigned int			wake_entry_type;
> 
> What about instead just create an anonymous structure of the two. That
> way they can still be randomized within the task struct and not be a
> target of attacks?
> 
> 	struct {
> 		struct llist_node	wake_entry;
> 		unsigned int		wake_entry_type;
> 	};
> 
> Would that work?

Yep, thanks, this works.
Will send v2 soon.

> -- Steve
> 
> 
> >  	int				on_cpu;
> >  #ifdef CONFIG_THREAD_INFO_IN_TASK
> >  	/* Current CPU: */
> 

-- 
Sincerely yours,
Mike.