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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 B33E6C432BE for ; Tue, 17 Aug 2021 20:24:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5957D604D7 for ; Tue, 17 Aug 2021 20:24:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5957D604D7 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 E7A9D8D0001; Tue, 17 Aug 2021 16:24:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E2AFA6B0072; Tue, 17 Aug 2021 16:24:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CF25F8D0001; Tue, 17 Aug 2021 16:24:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0049.hostedemail.com [216.40.44.49]) by kanga.kvack.org (Postfix) with ESMTP id B3B366B0071 for ; Tue, 17 Aug 2021 16:24:09 -0400 (EDT) Received: from smtpin32.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 5423F181DF756 for ; Tue, 17 Aug 2021 20:24:09 +0000 (UTC) X-FDA: 78485699418.32.DE2A412 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) by imf17.hostedemail.com (Postfix) with ESMTP id F06D7F0011E1 for ; Tue, 17 Aug 2021 20:24:08 +0000 (UTC) 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 AE11B1EC0556; Tue, 17 Aug 2021 22:24:03 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1629231843; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+yrW1YvDcJlPpXHuTQ1+89i5Y+U+96ERda2RQcSaGuw=; b=C1Bn0CPqvgGS5KpuudK22E1dJgTY5NTPkSI/Q5w0bDTkKQS0cynnWoc28EOwfoGfko1TrU us4DsxErEjkL3Gc0hHVcKYod7BmJDBUm0iGq5XjnZIed5vtQez3c/44kaZGK73NiO4Libs IYHHUABPOb4wMwNtsp9Lfvg7eUfxZtA= Date: Tue, 17 Aug 2021 22:24:47 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: "Yu, Yu-cheng" , 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: <1A27F5DF-477B-45B7-AD33-CC68D9B7CB89@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1A27F5DF-477B-45B7-AD33-CC68D9B7CB89@amacapital.net> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: F06D7F0011E1 X-Stat-Signature: w1jm9sgbepgdeoxgqxwb5k44stbx8bex Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=alien8.de header.s=dkim header.b=C1Bn0CPq; dmarc=pass (policy=none) header.from=alien8.de; spf=pass (imf17.hostedemail.com: domain of bp@alien8.de designates 5.9.137.197 as permitted sender) smtp.mailfrom=bp@alien8.de X-HE-Tag: 1629231848-707785 Content-Transfer-Encoding: quoted-printable 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 01:13:09PM -0700, Andy Lutomirski wrote: > > 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. > >=20 > > Hell, a shadow stack page is (Write=3D0, Dirty=3D1) so calling it wri= table > > ^^^^^^^ > > is simply wrong. >=20 > But it *is* writable using WRUSS, and it=E2=80=99s also writable by CAL= L, Well, if we have to be precise, CALL doesn't write it directly - it causes for shadow stack to be written as part of CALL's execution. Yeah yeah, potato potato. > WRSS, etc. Thus the "special kernel code" thing above. I've left it in instead of snipping it. > Now if the mm code tries to write protect it and expects sensible > semantics, the results could be interesting. At the very least, > someone would need to validate that RET reading a read only shadow > stack page does the right thing. Huh? A shadow stack page is RO (W=3D0). --=20 Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette