Re: [NEEDS-REVIEW] Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

[Yu, Yu-cheng]

On 9/15/2020 12:24 PM, Dave Hansen wrote:
> On 9/15/20 12:08 PM, Yu-cheng Yu wrote:
> > On Mon, 2020-09-14 at 17:12 -0700, Yu, Yu-cheng wrote:
> > > On 9/14/2020 7:50 AM, Dave Hansen wrote:
> > > > On 9/11/20 3:59 PM, Yu-cheng Yu wrote:
> > > > ...
> > > > > Here are the changes if we take the mprotect(PROT_SHSTK) approach.
> > > > > Any comments/suggestions?
> > > > I still don't like it. :)
> > > >
> > > > I'll also be much happier when there's a proper changelog to accompany
> > > > this which also spells out the alternatives any why they suck so much.
> > [...]
> >
> > I revised it.  If this turns out needing more work/discussion, we can split it
> > out from the shadow stack series.
>
> Where does that leave things?  You only get shadow stacks for
> single-threaded apps which have the ELF bits set?

As long as the system supports shadow stack, any application can 
mmap()/mprotect() a shadow stack.  A pthread can allocate a shadow stack 
too.  However, only shadow stack-enabled programs can activate/use the 
shadow stack.