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From:   Andy Lutomirski <luto@kernel.org>
Date:   Thu, 7 Jun 2018 09:28:05 -0700
Message-ID: <CALCETrWEeBbhGgJ2rVMAQGOK3BUuRSCWzuhmpO=WrmwO85Tnaw@mail.gmail.com>
Subject: Re: [PATCH 2/9] x86/cet: Add Kconfig option for user-mode shadow stack
To:     Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc:     Andrew Lutomirski <luto@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. J. Lu" <hjl.tools@gmail.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        mike.kravetz@oracle.com
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On Thu, Jun 7, 2018 at 9:02 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> On Thu, 2018-06-07 at 08:47 -0700, Andy Lutomirski wrote:
> > On Thu, Jun 7, 2018 at 7:40 AM Yu-cheng Yu <yu-cheng.yu@intel.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 :)
>
> Yes, I will remove changes in "arch/x86/entry/entry32.S".
> We still want to support x32/ia32 in the 64-bit kernel, right?
>

Yes, I think.  But that's not in entry_32.S


>