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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 55CB2C4320E for ; Tue, 17 Aug 2021 19:53:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3FF016023D for ; Tue, 17 Aug 2021 19:53:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229640AbhHQTyY (ORCPT ); Tue, 17 Aug 2021 15:54:24 -0400 Received: from mail.skyhub.de ([5.9.137.197]:60408 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233658AbhHQTyW (ORCPT ); Tue, 17 Aug 2021 15:54:22 -0400 Received: from zn.tnic (p200300ec2f117500b0ae8110978caeec.dip0.t-ipconnect.de [IPv6:2003:ec:2f11:7500:b0ae:8110:978c:aeec]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 9B1A41EC030F; Tue, 17 Aug 2021 21:53:42 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1629230022; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=aIPbkILpcrd+GjwKNb2Ar1grIyTzLxIuzU20uQTvckM=; b=YQJb4Z7vHcSycsuDkROq8+S722knun6LHl0bmKH2CQr5g1k7r8t8LVNTPXyMCk9n3OuN/4 edcppWeEwOk63eHEXk7sMxlSD4sqyIT6KK10prREwkg+OqHbMPuX16XGTwRXbGG459/Fz4 RKyzTHY9Gs2iFZ/pb7nwiX2YUpf4ll0= Date: Tue, 17 Aug 2021 21:54:21 +0200 From: Borislav Petkov To: "Yu, Yu-cheng" 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 , 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" , Dave Martin , Weijiang Yang , Pengfei Xu , Haitao Huang , Rick P Edgecombe , "Kirill A . Shutemov" Subject: Re: [PATCH v28 09/32] x86/mm: Introduce _PAGE_COW Message-ID: References: <20210722205219.7934-1-yu-cheng.yu@intel.com> <20210722205219.7934-10-yu-cheng.yu@intel.com> <59b9b98b-28e7-fc13-f13b-0079e184826f@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <59b9b98b-28e7-fc13-f13b-0079e184826f@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 17, 2021 at 11:24:29AM -0700, Yu, Yu-cheng wrote: > Indeed, this can be looked at in a few ways. We can visualize pte_write() > as 'CPU can write to it with MOV' or 'CPU can write to it with any opcodes'. > Depending on whatever pte_write() is, copy-on-write code can be adjusted > accordingly. Can be? I think you should exclude shadow stack pages from being writable and treat them as read-only. How the CPU writes them is immaterial - pte/pmd_write() is used by normal kernel code to query whether the page is writable or not by any instruction - not by the CPU. And since normal kernel code cannot write shadow stack pages, then for that code those pages are read-only. If special kernel code using shadow stack management insns needs to modify a shadow stack, then it can check whether a page is pte/pmd_shstk() but that code is special anyway. Hell, a shadow stack page is (Write=0, Dirty=1) so calling it writable ^^^^^^^ is simply wrong. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette