From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f199.google.com (mail-pl1-f199.google.com [209.85.214.199]) by kanga.kvack.org (Postfix) with ESMTP id 12D046B529B for ; Thu, 30 Aug 2018 13:58:43 -0400 (EDT) Received: by mail-pl1-f199.google.com with SMTP id bh1-v6so4341259plb.15 for ; Thu, 30 Aug 2018 10:58:43 -0700 (PDT) Received: from mga17.intel.com (mga17.intel.com. [192.55.52.151]) by mx.google.com with ESMTPS id e14-v6si6472434pff.332.2018.08.30.10.58.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Aug 2018 10:58:42 -0700 (PDT) Message-ID: <1535651666.27823.6.camel@intel.com> Subject: Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW From: Yu-cheng Yu Date: Thu, 30 Aug 2018 10:54:26 -0700 In-Reply-To: <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> References: <20180830143904.3168-1-yu-cheng.yu@intel.com> <20180830143904.3168-13-yu-cheng.yu@intel.com> <079a55f2-4654-4adf-a6ef-6e480b594a2f@linux.intel.com> <1535649960.26689.15.camel@intel.com> <33d45a12-513c-eba2-a2de-3d6b630e928e@linux.intel.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen , Jann Horn Cc: the arch/x86 maintainers , "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , kernel list , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Florian Weimer , hjl.tools@gmail.com, Jonathan Corbet , keescook@chromiun.org, Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com On Thu, 2018-08-30 at 10:33 -0700, Dave Hansen wrote: > On 08/30/2018 10:26 AM, Yu-cheng Yu wrote: > > > > We don't have the guard page now, but there is a shadow stack > > token > > there, which cannot be used as a return address. > The overall concern is that we could overflow into a page that we > did > not intend.A A Either another actual shadow stack or something that a > page > that the attacker constructed, like the transient scenario Jann > described. > A task could go beyond the bottom of its shadow stack by doing either 'ret' or 'incssp'. A If it is the 'ret' case, the token prevents it. A If it is the 'incssp' case, a guard page cannot prevent it entirely, right? Yu-cheng