[kernel-hardening] Re: [PATCH] fork: Allow stack to be wiped on fork

[Jiri Kosina <jikos@kernel.org>]

On Fri, 26 Jan 2018, Jiri Kosina wrote:

> > diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> > index 34f053a150a9..091f53fe31cc 100644
> > --- a/include/linux/thread_info.h
> > +++ b/include/linux/thread_info.h
> > @@ -43,7 +43,9 @@ enum {
> >  #define THREAD_ALIGN	THREAD_SIZE
> >  #endif
> >  
> > -#if IS_ENABLED(CONFIG_DEBUG_STACK_USAGE) || IS_ENABLED(CONFIG_DEBUG_KMEMLEAK)
> > +#if IS_ENABLED(CONFIG_DEBUG_STACK_USAGE) || \
> > +    IS_ENABLED(CONFIG_DEBUG_KMEMLEAK) || \
> > +    IS_ENABLED(CONFIG_CLEAR_STACK_FORK)
> >  # define THREADINFO_GFP		(GFP_KERNEL_ACCOUNT | __GFP_ZERO)
> >  #else
> >  # define THREADINFO_GFP		(GFP_KERNEL_ACCOUNT)
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 2295fc69717f..215b1ce2b2cd 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -215,7 +215,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
> >  		if (!s)
> >  			continue;
> >  
> > -#ifdef CONFIG_DEBUG_KMEMLEAK
> > +#if IS_ENABLED(CONFIG_DEBUG_KMEMLEAK) || IS_ENABLED(CONFIG_CLEAR_STACK_FORK)
> >  		/* Clear stale pointers from reused stack. */
> >  		memset(s->addr, 0, THREAD_SIZE);
> >  #endif
> 
> Is there any good reason not to do it symmetricaly also for non-vmapped 
> stacks? (by passing __GFP_ZERO to alloc_pages_node())?

Ah, of course you already do by extending THREADINFO_GFP, sorry for the 
noise.

-- 
Jiri Kosina