linux-kernel - Re: [PATCH] x86/mpx: pass 'mm' to kernel_managing_mpx_tables() in mpx_notify

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Date:   Mon, 3 Dec 2018 16:54:43 -0800
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, luto@...nel.org,
        peterz@...radead.org
Subject: Re: [PATCH] x86/mpx: pass 'mm' to kernel_managing_mpx_tables() in
 mpx_notify_unmap()

On Mon, Dec 03, 2018 at 12:49:44PM -0800, Dave Hansen wrote:
> On 12/3/18 12:43 PM, Jarkko Sakkinen wrote:
> > If mm is not the same as current->mm, mpx_notify_unmap() will yield
> > invalid results and at worst will lead to a crash if it gets called by
> > a kthread.
> 
> It's also worth noting that this does not fix any actual,
> end-user-visible bug today.  It really only prepares the code for the
> case where it is called for a different mm than current->mm.
> 
> > --- a/arch/x86/mm/mpx.c
> > +++ b/arch/x86/mm/mpx.c
> > @@ -882,7 +882,7 @@ static int mpx_unmap_tables(struct mm_struct *mm,
> >   * necessary, and the 'vma' is the first vma in this range (start -> end).
> >   */
> >  void mpx_notify_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
> > -		unsigned long start, unsigned long end)
> > +		      unsigned long start, unsigned long end)
> >  {
> >  	int ret;
> 
> Please leave superfluous whitespace changes out of these things.
> 
> But, otherwise, this looks fine.
> 
> > Fixes: 1de4fa14ee25 ("x86, mpx: Cleanup unused bound tables")
> 
> FWIW, I'm not sure you should be submitting this separately from your
> SGX series.  The deferred unmapping is really the thing that requires
> the code to be changed.

Thank you for the feedback. I'll include this to the next revision of the
SGX patch set and explain why the change is needed.

/Jarkko