Re: [PATCH 2/9] x86/cet: Add Kconfig option for user-mode shadow stack

[Andy Lutomirski]

On Thu, Jun 7, 2018 at 7:40 AM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
>
> Introduce Kconfig option X86_INTEL_SHADOW_STACK_USER.
>
> An application has shadow stack protection when all the following are
> true:
>
>   (1) The kernel has X86_INTEL_SHADOW_STACK_USER enabled,
>   (2) The running processor supports the shadow stack,
>   (3) The application is built with shadow stack enabled tools & libs
>       and, and at runtime, all dependent shared libs can support shadow
>       stack.
>
> If this kernel config option is enabled, but (2) or (3) above is not
> true, the application runs without the shadow stack protection.
> Existing legacy applications will continue to work without the shadow
> stack protection.
>
> The user-mode shadow stack protection is only implemented for the
> 64-bit kernel.  Thirty-two bit applications are supported under the
> compatibility mode.
>

The 64-bit only part seems entirely reasonable.  So please make the
code 64-bit only :)