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

Kees Cook
2021-02-05T18:26:58Z

On Thu, Feb 04, 2021 at 03:41:59PM -0800, Yu, Yu-cheng wrote:
> 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?

Ah, good point. Yes, since that's a bitmap it ends up describing what
follows. This is fine as-is. Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

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Kees Cook