Re: [PATCH v19 24/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

["Yu, Yu-cheng" <yu-cheng.yu@xxxxxxxxx>]

On 2/4/2021 12:35 PM, Kees Cook wrote:
> On Wed, Feb 03, 2021 at 02:55:46PM -0800, Yu-cheng Yu wrote:
> > arch_prctl(ARCH_X86_CET_STATUS, u64 *args)
> >      Get CET feature status.
> >
> >      The parameter 'args' is a pointer to a user buffer.  The kernel returns
> >      the following information:
> >
> >      *args = shadow stack/IBT status
> >      *(args + 1) = shadow stack base address
> >      *(args + 2) = shadow stack size
>
> What happens if this needs to grow in the future? Should the first u64
> contain the array size?
>
> Otherwise, looks sensible.
>
> -Kees

The first item is a bitmap, and there are two possible bits.  Should 
there be a need, we can then do things about it.  My thought at the 
moment is, we may not meet the situation.  Can we keep this for now?

--
Yu-cheng