From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-6.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=unavailable autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id B57827D08A for ; Tue, 14 Aug 2018 21:29:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730883AbeHOASU (ORCPT ); Tue, 14 Aug 2018 20:18:20 -0400 Received: from mga05.intel.com ([192.55.52.43]:10599 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725877AbeHOAST (ORCPT ); Tue, 14 Aug 2018 20:18:19 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 14 Aug 2018 14:29:14 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.53,240,1531810800"; d="scan'208";a="80299382" Received: from 2b52.sc.intel.com ([143.183.136.51]) by fmsmga004.fm.intel.com with ESMTP; 14 Aug 2018 14:29:15 -0700 Message-ID: <1534282125.24160.9.camel@intel.com> Subject: Re: [RFC PATCH v2 13/27] mm: Handle shadow stack page fault From: Yu-cheng Yu To: Peter Zijlstra , Dave Hansen Cc: 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 , Cyrill Gorcunov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , "Ravi V. Shankar" , Vedvyas Shanbhogue Date: Tue, 14 Aug 2018 14:28:45 -0700 In-Reply-To: <20180711090656.GS2476@hirez.programming.kicks-ass.net> References: <20180710222639.8241-1-yu-cheng.yu@intel.com> <20180710222639.8241-14-yu-cheng.yu@intel.com> <2f3ff321-c629-3e00-59f6-8bca510650d4@linux.intel.com> <20180711090656.GS2476@hirez.programming.kicks-ass.net> 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-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, 2018-07-11 at 11:06 +0200, Peter Zijlstra wrote: > On Tue, Jul 10, 2018 at 04:06:25PM -0700, Dave Hansen wrote: > > > > On 07/10/2018 03:26 PM, Yu-cheng Yu wrote: > > > > > > + if (is_shstk_mapping(vma->vm_flags)) > > > + entry = pte_mkdirty_shstk(entry); > > > + else > > > + entry = pte_mkdirty(entry); > > > + > > > + entry = maybe_mkwrite(entry, vma); > > >   if (ptep_set_access_flags(vma, vmf->address, vmf->pte, > > > entry, 1)) > > >   update_mmu_cache(vma, vmf->address, vmf->pte); > > >   pte_unmap_unlock(vmf->pte, vmf->ptl); > > > @@ -2526,7 +2532,11 @@ static int wp_page_copy(struct vm_fault > > > *vmf) > > >   } > > >   flush_cache_page(vma, vmf->address, > > > pte_pfn(vmf->orig_pte)); > > >   entry = mk_pte(new_page, vma->vm_page_prot); > > > - entry = maybe_mkwrite(pte_mkdirty(entry), vma); > > > + if (is_shstk_mapping(vma->vm_flags)) > > > + entry = pte_mkdirty_shstk(entry); > > > + else > > > + entry = pte_mkdirty(entry); > > > + entry = maybe_mkwrite(entry, vma); > > Do we want to lift this hunk of code and put it elsewhere?  Maybe: > > > > entry = pte_set_vma_features(entry, vma); > > > > and then: > > > > pte_t pte_set_vma_features(pte_t entry, struct vm_area_struct) > > { > > /* > >  * Shadow stack PTEs are always dirty and always > >  * writable.  They have a different encoding for > >  * this than normal PTEs, though. > >  */ > > if (is_shstk_mapping(vma->vm_flags)) > > entry = pte_mkdirty_shstk(entry); > > else > > entry = pte_mkdirty(entry); > > > > entry = maybe_mkwrite(entry, vma); > > > > return entry; > > } > Yes, that wants a helper like that. Not sold on the name, but > whatever. > > Is there any way we can hide all the shadow stack magic in arch > code? We use is_shstk_mapping() only to determine PAGE_DIRTY_SW or PAGE_DIRTY_HW should be set in a PTE.  One way to remove this shadow stack code from generic code is changing pte_mkdirty(pte) to pte_mkdirty(pte, vma), and in the arch code we handle shadow stack. Is this acceptable? Thanks, Yu-cheng