From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DDA66C3F2D2 for ; Thu, 5 Mar 2020 20:38:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B9B972146E for ; Thu, 5 Mar 2020 20:38:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726080AbgCEUiR (ORCPT ); Thu, 5 Mar 2020 15:38:17 -0500 Received: from mga07.intel.com ([134.134.136.100]:46441 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725991AbgCEUiR (ORCPT ); Thu, 5 Mar 2020 15:38:17 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Mar 2020 12:38:16 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,519,1574150400"; d="scan'208";a="229822632" Received: from yyu32-desk.sc.intel.com ([143.183.136.146]) by orsmga007.jf.intel.com with ESMTP; 05 Mar 2020 12:38:15 -0800 Message-ID: <607b3094a06dd62dfabb0fd6991429f464355a0c.camel@intel.com> Subject: Re: [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection From: Yu-cheng Yu To: Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , x86-patch-review@intel.com Date: Thu, 05 Mar 2020 12:38:14 -0800 In-Reply-To: <597fb45a-cb94-e8e7-8e80-45a26766d32a@intel.com> References: <20200205181935.3712-1-yu-cheng.yu@intel.com> <20200205181935.3712-6-yu-cheng.yu@intel.com> <597fb45a-cb94-e8e7-8e80-45a26766d32a@intel.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.4 (3.32.4-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-api-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Wed, 2020-02-26 at 09:03 -0800, Dave Hansen wrote: > On 2/5/20 10:19 AM, Yu-cheng Yu wrote: > > Introduce Kconfig option: X86_INTEL_SHADOW_STACK_USER. > > > > Shadow Stack (SHSTK) provides protection against function return address > > corruption. It is active when the kernel has this feature enabled, and > > both the processor and the application support it. When this feature is > > enabled, legacy non-SHSTK applications continue to work, but without SHSTK > > protection. > > > > The user-mode SHSTK protection is only implemented for the 64-bit kernel. > > IA32 applications are supported under the compatibility mode. > > I think what you're trying to say here is that the hardware supports > shadow stacks with 32-bit kernels. However, this series does not > include that support and we have no plans to add it. > > Right? Yes. > > I'll let others weigh in, but I rather dislike the use of acronyms here. > I'd much rather see the english "shadow stack" everywhere than SHSTK. I will change to shadow stack. > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index 5e8949953660..6c34b701c588 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -1974,6 +1974,28 @@ config X86_INTEL_TSX_MODE_AUTO > > side channel attacks- equals the tsx=auto command line parameter. > > endchoice > > > > +config X86_INTEL_CET > > + def_bool n > > + > > +config ARCH_HAS_SHSTK > > + def_bool n > > + > > +config X86_INTEL_SHADOW_STACK_USER > > + prompt "Intel Shadow Stack for user-mode" > > Nit: this whole thing is to support more than a single stack. I'd make > this plural at least in the text: "shadow stacks". OK. > > > + def_bool n > > + depends on CPU_SUP_INTEL && X86_64 > > + select ARCH_USES_HIGH_VMA_FLAGS > > + select X86_INTEL_CET > > + select ARCH_HAS_SHSTK > > + ---help--- > > + Shadow Stack (SHSTK) provides protection against program > > + stack corruption. It is active when the kernel has this > > + feature enabled, and the processor and the application > > + support it. When this feature is enabled, legacy non-SHSTK > > + applications continue to work, but without SHSTK protection. > > + > > + If unsure, say y. > > This is missing a *lot* of information. > > What matters to someone turning this on? > > 1. It's a hardware feature. This only matters if you have the right > hardware > 2. It's a security hardening feature. You dance around this, but need > to come out and say it. > 3. Apps must be enabled to use it. You get no protection "for free" on > old userspace. > 4. The hardware supports user and kernel, but this option is for > userspace only. I will update the help text. Yu-cheng