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

From: Andy Lutomirski <luto@kernel.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: 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
Subject: Re: [PATCH 2/9] x86/cet: Add Kconfig option for user-mode shadow stack
Date: Thu, 7 Jun 2018 08:47:28 -0700	[thread overview]
Message-ID: <CALCETrWwGCZ+Fbk+O8T6S48teHj60bQQiHQ49=SsKUOpm8VLBA@mail.gmail.com> (raw)
In-Reply-To: <20180607143705.3531-3-yu-cheng.yu@intel.com>

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 :)