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_PASS,URIBL_BLOCKED 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 B465EC433F4 for ; Thu, 30 Aug 2018 20:57:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 75CF82083C for ; Thu, 30 Aug 2018 20:57:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 75CF82083C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727532AbeHaBBD (ORCPT ); Thu, 30 Aug 2018 21:01:03 -0400 Received: from mga18.intel.com ([134.134.136.126]:3121 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726690AbeHaBBD (ORCPT ); Thu, 30 Aug 2018 21:01:03 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 30 Aug 2018 13:57:01 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,308,1531810800"; d="scan'208";a="253278023" Received: from 2b52.sc.intel.com ([143.183.136.52]) by orsmga005.jf.intel.com with ESMTP; 30 Aug 2018 13:57:00 -0700 Message-ID: <1535662366.28781.6.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 To: Jann Horn Cc: Dave Hansen , 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 Date: Thu, 30 Aug 2018 13:52:46 -0700 In-Reply-To: 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> <1535651666.27823.6.camel@intel.com> <1535660494.28258.36.camel@intel.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.18.5.2-0ubuntu3.2 Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-08-30 at 22:44 +0200, Jann Horn wrote: > On Thu, Aug 30, 2018 at 10:25 PM Yu-cheng Yu > wrote: ... > > In the flow you described, if C writes to the overflow page before > > B > > gets in with a 'call', the return address is still correct for > > B.  To > > make an attack, C needs to write again before the TLB flush.  I > > agree > > that is possible. > > > > Assume we have a guard page, can someone in the short window do > > recursive calls in B, move ssp to the end of the guard page, and > > trigger the same again?  He can simply take the incssp route. > I don't understand what you're saying. If the shadow stack is > between > guard pages, you should never be able to move SSP past that area's > guard pages without an appropriate shadow stack token (not even with > INCSSP, since that has a maximum range of PAGE_SIZE/2), and > therefore, > it shouldn't matter whether memory outside that range is incorrectly > marked as shadow stack. Am I missing something? INCSSP has a range of 256, but we can do multiple of that. But I realize the key is not to have the transient SHSTK page at all. The guard page is !pte_write() and even we have flaws in ptep_set_wrprotect(), there will not be any transient SHSTK pages. I will add guard pages to both ends. Still thinking how to fix ptep_set_wrprotect(). Yu-cheng