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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 B6458C4363D for ; Wed, 7 Oct 2020 10:20:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5A98420870 for ; Wed, 7 Oct 2020 10:20:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728139AbgJGKUl (ORCPT ); Wed, 7 Oct 2020 06:20:41 -0400 Received: from foss.arm.com ([217.140.110.172]:41422 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728102AbgJGKUW (ORCPT ); Wed, 7 Oct 2020 06:20:22 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7B3FB11B3; Wed, 7 Oct 2020 03:20:21 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7B80F3F71F; Wed, 7 Oct 2020 03:20:19 -0700 (PDT) Date: Wed, 7 Oct 2020 11:20:16 +0100 From: Dave Martin To: Dave Hansen Cc: "H.J. Lu" , "Chang S. Bae" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , the arch/x86 maintainers , Len Brown , Michael Ellerman , Tony Luck , "Ravi V. Shankar" , GNU C Library , linux-arch , Linux API , LKML Subject: Re: [RFC PATCH 0/4] x86: Improve Minimum Alternate Stack Size Message-ID: <20201007102015.GG6642@arm.com> References: <20200929205746.6763-1-chang.seok.bae@intel.com> <20201005134534.GT6642@arm.com> <20201006092532.GU6642@arm.com> <20201006152553.GY6642@arm.com> <7663eff0-6c94-f6bf-f3e2-93ede50e75ed@intel.com> <20201006170020.GB6642@arm.com> <3545e3f3-a716-5e82-bd24-450eb74b4563@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3545e3f3-a716-5e82-bd24-450eb74b4563@intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 06, 2020 at 11:30:42AM -0700, Dave Hansen wrote: > On 10/6/20 10:00 AM, Dave Martin wrote: > > On Tue, Oct 06, 2020 at 08:33:47AM -0700, Dave Hansen wrote: > >> On 10/6/20 8:25 AM, Dave Martin wrote: > >>> Or are people reporting real stack overruns on x86 today? > >> We have real overruns. We have ~2800 bytes of XSAVE (regisiter) state > >> mostly from AVX-512, and a 2048 byte MINSIGSTKSZ. > > Right. Out of interest, do you believe that's a direct consequence of > > the larger kernel-generated signal frame, or does the expansion of > > userspace stack frames play a role too? > > The kernel-generated signal frame is entirely responsible for the ~2800 > bytes that I'm talking about. > > I'm sure there are some systems where userspace plays a role, but those > are much less of a worry at the moment, since the kernel-induced > overflows mean an instant crash that userspace has no recourse for. Ack, that sounds pretty convincing. Cheers ---Dave