From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-4.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id B58EA1F4B4 for ; Wed, 7 Oct 2020 10:20:25 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id AF4E9386191F; Wed, 7 Oct 2020 10:20:24 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org AF4E9386191F DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1602066024; bh=EjlDcao8CF9HZ4JjBqgI5Gt7CsFtwoBb+21SYX5Jz1o=; h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=RWWaHAuBHayuD6quj38VD+01vLu3LfQkFVmdQGUZH2jyFLBY58Qsq0WQI/VJtPXAe qh5v208mei3ys/kG0tn2sscJWPeDvBSmVlTXOsXzyrKgCn4GzJdGpCs6OSp955vxz2 5lgRLhKW7v3afgScQie41+lvNDkcQ3lXq0xmuzRs= Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id DF9343857C45 for ; Wed, 7 Oct 2020 10:20:21 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org DF9343857C45 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 To: Dave Hansen 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) X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Dave Martin via Libc-alpha Reply-To: Dave Martin Cc: linux-arch , Tony Luck , GNU C Library , "Ravi V. Shankar" , Len Brown , "Chang S. Bae" , the arch/x86 maintainers , LKML , Andy Lutomirski , Linux API , Thomas Gleixner , Borislav Petkov , Ingo Molnar Errors-To: libc-alpha-bounces@sourceware.org Sender: "Libc-alpha" 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