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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 D2DC1C31E4D for ; Fri, 14 Jun 2019 15:33:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B59162175B for ; Fri, 14 Jun 2019 15:33:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726772AbfFNPdW (ORCPT ); Fri, 14 Jun 2019 11:33:22 -0400 Received: from mga18.intel.com ([134.134.136.126]:64871 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725780AbfFNPdV (ORCPT ); Fri, 14 Jun 2019 11:33:21 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Jun 2019 08:33:20 -0700 X-ExtLoop1: 1 Received: from yyu32-desk1.sc.intel.com ([10.144.153.205]) by fmsmga001.fm.intel.com with ESMTP; 14 Jun 2019 08:33:20 -0700 Message-ID: Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function From: Yu-cheng Yu To: Dave Hansen , Andy Lutomirski Cc: Peter Zijlstra , 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 , 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 , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin Date: Fri, 14 Jun 2019 08:25:16 -0700 In-Reply-To: References: <20190606200926.4029-1-yu-cheng.yu@intel.com> <20190606200926.4029-4-yu-cheng.yu@intel.com> <20190607080832.GT3419@hirez.programming.kicks-ass.net> <20190607174336.GM3436@hirez.programming.kicks-ass.net> <34E0D316-552A-401C-ABAA-5584B5BC98C5@amacapital.net> <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com> <25281DB3-FCE4-40C2-BADB-B3B05C5F8DD3@amacapital.net> <3f19582d-78b1-5849-ffd0-53e8ca747c0d@intel.com> <5aa98999b1343f34828414b74261201886ec4591.camel@intel.com> <0665416d-9999-b394-df17-f2a5e1408130@intel.com> <5c8727dde9653402eea97bfdd030c479d1e8dd99.camel@intel.com> <328275c9b43c06809c9937c83d25126a6e3efcbd.camel@intel.com> <92e56b28-0cd4-e3f4-867b-639d9b98b86c@intel.com> <1b961c71d30e31ecb22da2c5401b1a81cb802d86.camel@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-06-10 at 15:59 -0700, Dave Hansen wrote: > On 6/10/19 3:40 PM, Yu-cheng Yu wrote: > > Ok, we will go back to do_mmap() with MAP_PRIVATE, MAP_NORESERVE and > > VM_DONTDUMP. The bitmap will cover only 48-bit address space. > > Could you make sure to discuss the downsides of only doing a 48-bit > address space? The downside is that we cannot load legacy lib's above 48-bit address space, but currently ld-linux does not do that. Should ld-linux do that in the future, dlopen() fails. Considering CRIU migration, we probably need to do this anyway? > What are the reasons behind and implications of VM_DONTDUMP? The bitmap is very big. In GDB, it should be easy to tell why a control-protection fault occurred without the bitmap. Yu-cheng