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SubjectRe: [RFC PATCH v2 15/27] mm/mprotect: Prevent mprotect from changing shadow stack
On Tue, Jul 10, 2018 at 04:10:08PM -0700, Dave Hansen wrote:
> On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
>
> This still needs a changelog, even if you think it's simple.
> > --- a/mm/mprotect.c
> > +++ b/mm/mprotect.c
> > @@ -446,6 +446,15 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
> > error = -ENOMEM;
> > if (!vma)
> > goto out;
> > +
> > + /*
> > + * Do not allow changing shadow stack memory.
> > + */
> > + if (vma->vm_flags & VM_SHSTK) {
> > + error = -EINVAL;
> > + goto out;
> > + }
> > +
>
> I think this is a _bit_ draconian. Why shouldn't we be able to use
> protection keys with a shadow stack? Or, set it to PROT_NONE?

Right, and then there's also madvise() and some of the other accessors.

Why do we need to disallow this? AFAICT the worst that can happen is
that a process wrecks itself, so what?

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