Re: [PATCH 09/10] mm: Prevent madvise from changing shadow stack

[Yu-cheng Yu]

On Thu, 2018-06-07 at 14:09 -0700, Nadav Amit wrote:
> Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
> 
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> > ---
> > mm/madvise.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> > 
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 4d3c922ea1a1..2a6988badd6b 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -839,6 +839,14 @@ SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
> > 	if (vma && start > vma->vm_start)
> > 		prev = vma;
> > 
> > +	/*
> > +	 * Don't do anything on shadow stack.
> > +	 */
> > +	if (vma->vm_flags & VM_SHSTK) {
> > +		error = -EINVAL;
> > +		goto out_no_plug;
> > +	}
> > +
> > 	blk_start_plug(&plug);
> > 	for (;;) {
> > 		/* Still start < end. */
> 
> What happens if the madvise() revolves multiple VMAs, the first one is not
> VM_SHSTK, but the another one is? Shouldnât the test be done inside the
> loop, potentially in madvise_vma() ?
> 

I will fix it.  Thanks!