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

[Yu, Yu-cheng]

On 8/25/2020 12:19 PM, Dave Hansen wrote:
> On 8/25/20 11:43 AM, Yu, Yu-cheng wrote:
> > > > arch_prctl(ARCH_X86_CET_MMAP_SHSTK, u64 *args)
> > > >       Allocate a new shadow stack.
> > > >
> > > >       The parameter 'args' is a pointer to a user buffer.
> > > >
> > > >       *args = desired size
> > > >       *(args + 1) = MAP_32BIT or MAP_POPULATE
> > > >
> > > >       On returning, *args is the allocated shadow stack address.
> > >
> > > This is hideous.  Would this be better as a new syscall?
> >
> > Could you point out why this is hideous, so that I can modify the
> > arch_prctl?
>
> Passing values in memory is hideous when we don't have to.  A syscall
> would let you have separate arguments for size and flags and would also
> let you have a nice return value instead of needing to do that in memory
> too.

That is a good justification.

> > I think this is more arch-specific.  Even if it becomes a new syscall,
> > we still need to pass the same parameters.
>
> Right, but without the copying in and out of memory.
Linux-api is already on the Cc list.  Do we need to add more people to 
get some agreements for the syscall?