Re: [patch V2 2/2] x86/ldt: Prevent ldt inheritance on exec

[Thomas Gleixner]

On Mon, 11 Dec 2017, Peter Zijlstra wrote:
> On Sat, Dec 09, 2017 at 07:24:35PM +0100, Thomas Gleixner wrote:
> > On Fri, 8 Dec 2017, Thomas Gleixner wrote:
> > > +int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm)
> > >  {
> > >  	struct ldt_struct *new_ldt;
> > > -	struct mm_struct *old_mm;
> > >  	int retval = 0;
> > >  
> > > -	mutex_init(&mm->context.lock);
> > > -	old_mm = current->mm;
> > > -	if (!old_mm) {
> > > -		mm->context.ldt = NULL;
> > > +	if (!old_mm)
> > >  		return 0;
> > > -	}
> > >  
> > >  	mutex_lock(&old_mm->context.lock);
> > 
> > Bah. That's broken. It now nests into old_mm->mmap_sem which is the reverse
> > lock order than in ldt_write. Will fix.
> 
> But read_ldt() will still nest mmap_sem inside context.lock, no? Lockdep
> doesn't care about old_mm vs new_mm.

Yeah, found that and fixed that already. Next version will be perfect :)