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

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Message-ID: <alpine.DEB.2.20.1712091927320.2301@nanos>
Date:   Sat, 9 Dec 2017 19:28:31 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
cc:     Linus Torvalds <torvalds@...uxfoundation.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch V2 2/2] x86/ldt: Prevent ldt inheritance on exec

On Sat, 9 Dec 2017, 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.

Confused myself. mmap_sem is not taken in mainline ldt_write. It's just in
the stuff I'm working on.

Thanks,

	tglx