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 2D8C3C4320A for ; Fri, 27 Aug 2021 18:46:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 06DDA61008 for ; Fri, 27 Aug 2021 18:46:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230186AbhH0Sqs (ORCPT ); Fri, 27 Aug 2021 14:46:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229882AbhH0Sqs (ORCPT ); Fri, 27 Aug 2021 14:46:48 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA57DC061757; Fri, 27 Aug 2021 11:45:58 -0700 (PDT) Received: from zn.tnic (p200300ec2f111700cf40790d4c46ba75.dip0.t-ipconnect.de [IPv6:2003:ec:2f11:1700:cf40:790d:4c46:ba75]) (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 645881EC0464; Fri, 27 Aug 2021 20:45:53 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1630089953; 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=y0FEGpbT1o/usEWCQaIVd7WpX4gpA+I5TcpFa2iPS/c=; b=SHMA6G9AjxgkvlDD605FGB3xhf0BjvRxxmOo92lMF2ekx955Tjyy8uY4UbXlI7oyLe209g +JYuyJ2G360w9la3Fo0zaixmBftxHU0YDrMyaPumDFptRiuMFfbh/CP3tYATF87eJSLSql PtdHSUjwg7HnCzJzHi1aVTBWqnFKAak= Date: Fri, 27 Aug 2021 20:46:35 +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 Subject: Re: [PATCH v29 23/32] x86/cet/shstk: Add user-mode shadow stack support Message-ID: References: <20210820181201.31490-1-yu-cheng.yu@intel.com> <20210820181201.31490-24-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Fri, Aug 27, 2021 at 11:37:34AM -0700, Yu, Yu-cheng wrote: > Right now, the kernel does lazy restore, and it waits until right before a > task goes back to ring-3 to restore xstates. If a task needs to write to > any xstate registers before that (e.g. for signals), it restores the whole > xstates first and clears TIF_NEED_FPU_LOAD, which will prevent xstates being > restored again later. shstk_setup() allocates a shadow stack for the task and puts its pointer in MSR_IA32_PL3_SSP. What does that have to do with a task having to write any xstate registers? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette