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 9405FC4320A for ; Tue, 17 Aug 2021 21:00:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 18EB761042 for ; Tue, 17 Aug 2021 21:00:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 18EB761042 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=alien8.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 529A26B0071; Tue, 17 Aug 2021 17:00:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4DA088D0001; Tue, 17 Aug 2021 17:00:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3A1C86B0073; Tue, 17 Aug 2021 17:00:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0070.hostedemail.com [216.40.44.70]) by kanga.kvack.org (Postfix) with ESMTP id 1DFC76B0071 for ; Tue, 17 Aug 2021 17:00:46 -0400 (EDT) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id BDF6E231C4 for ; Tue, 17 Aug 2021 21:00:45 +0000 (UTC) X-FDA: 78485791650.13.5060D4D Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by imf03.hostedemail.com (Postfix) with ESMTP id 64A2B30039AA for ; Tue, 17 Aug 2021 21:00:45 +0000 (UTC) Received: from zn.tnic (p200300ec2f1175002d6ed1db7aad8219.dip0.t-ipconnect.de [IPv6:2003:ec:2f11:7500:2d6e:d1db:7aad:8219]) (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 ECBC61EC054F; Tue, 17 Aug 2021 23:00:39 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1629234040; 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=mXsfggRjwQDlm0H7Ke4Yg4s+PjvD0gM8YpelP0TsXHU=; b=h50TDWS4H9GdDodATzIk47AkyXvA4xxH+tNY8zodUJbiv66vz2uFecq8W13pkePmohzcG+ 9bTxxFbcNJNR6KjEBv4mabKrZU3gRqlEIj14TxD1Hrp0arnMYTBjLNHIqwAoViz5K4MhkU 9jeBsoXMtMB5jcgWi4P1gXtqA77We3I= Date: Tue, 17 Aug 2021 23:01:18 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: "luto@amacapital.net" , Yu-cheng Yu , the arch/x86 maintainers , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Linux Kernel Mailing List , linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Linux API , Arnd Bergmann , 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 (Intel)" , Randy Dunlap , "Shankar, Ravi V" , 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: <1A27F5DF-477B-45B7-AD33-CC68D9B7CB89@amacapital.net> <490345b6-3e3d-4692-8162-85dcb71434c9@www.fastmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <490345b6-3e3d-4692-8162-85dcb71434c9@www.fastmail.com> Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=alien8.de header.s=dkim header.b=h50TDWS4; dmarc=pass (policy=none) header.from=alien8.de; spf=pass (imf03.hostedemail.com: domain of bp@alien8.de designates 5.9.137.197 as permitted sender) smtp.mailfrom=bp@alien8.de X-Stat-Signature: ry3h93xp3uhjnj3781rgqch3k57rjtjs X-Rspamd-Queue-Id: 64A2B30039AA X-Rspamd-Server: rspam05 X-HE-Tag: 1629234045-640670 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Aug 17, 2021 at 01:51:52PM -0700, Andy Lutomirski wrote: > WRSS can be used from user mode depending on the configuration. My point being, if you're going to do shadow stack management operations, you should check whether the target you're writing to is a shadow stack page. Clearly userspace can't do that but userspace will get notified of that pretty timely. > Double-you shmouble-you. You can't write it with MOV, but you can > write it from user code and from kernel code. As far as the mm is > concerned, I think it should be considered writable. Because? > Although... anyone who tries to copy_to_user() it is going to be a bit > surprised. Hmm. Ok, so you see the confusion. In any case, I don't think you can simply look at a shadow stack page as simple writable page. There are cases where it is going to be fun. So why are we even saying that a shadow stack page is writable? Why can't we simply say that a shadow stack page is, well, something special? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette