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

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Date:   Thu, 7 Jun 2018 08:47:28 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        mike.kravetz@...cle.com
Subject: Re: [PATCH 2/9] x86/cet: Add Kconfig option for user-mode shadow stack

On Thu, Jun 7, 2018 at 7:40 AM Yu-cheng Yu <yu-cheng.yu@...el.com> 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 :)