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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 2F017C47254 for ; Tue, 5 May 2020 13:57:26 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id EDADA206A5 for ; Tue, 5 May 2020 13:57:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Qldix5U+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EDADA206A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:60038 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jVy4b-0006AL-4P for qemu-devel@archiver.kernel.org; Tue, 05 May 2020 09:57:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53024) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jVy3N-0004uW-OM for qemu-devel@nongnu.org; Tue, 05 May 2020 09:56:09 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:39896 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jVy3M-00030O-Pl for qemu-devel@nongnu.org; Tue, 05 May 2020 09:56:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588686968; 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=GqjJKj8vl5w2nF+/ZoGSPZtf7fkexGsWEfDvmSN8bf0=; b=Qldix5U+NQtbhry83Lxvc22NBsY5Vi5hSfV2C4Pwpm6mxM7lZzshlSOY9LfsdDWreZx160 lfeKu4Z0wcbsls2Xpzlo+MpU+fKGePk/DO2iH8uo+mdvJzYEIuj0ItJUdshZGi6CJ0Uyi7 6gvq+Qtno7bi5bWJrv5482qfeXo73RM= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-287-ZRl3PRPVMLeTDKH-J6VZgA-1; Tue, 05 May 2020 09:56:03 -0400 X-MC-Unique: ZRl3PRPVMLeTDKH-J6VZgA-1 Received: by mail-wr1-f72.google.com with SMTP id v17so1240001wrq.8 for ; Tue, 05 May 2020 06:56:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=Odo0HaRODgXKYRiDbnYesTbfQvkc1Oe3VZx7d1vIliU=; b=U60NKubJSBjKT0EbAHz7Nx9K9nx2AtFCj+IIhGBkfiYx7+jGf1KvZNRUq1ONshB8oK xgmkC2j2BkBnG4KAqohH1QSH4O0hNfObs1ouHn3R5d0pSqfKYxCBvTZlLpleeH4ZMLx+ HEdrjFDZOPm6NJZ1UmddXtN//NT1BBUmOngyS/y+tcxlKpY+vEdfcbIlF7BUYrXP33Vt mKRvKP56s+Q7AYaJ5u19nPr+X3wSrTygMPLiLQ6GViHWr1AMTaGP4CXQV5q+6hcpjVuq XDMmsDIreXruyWCELhb1DAApJ8Ftm/oHb25GszwSfz1IWHy9MrvbGotfn9ZA4+15HRSP 1oSQ== X-Gm-Message-State: AGi0Pubg04/URcU+bg9YnWaIqHsrsyCKgkRUuyWNMkHrNGEoYXXBmEm3 014hKZAEmyEFnMCYKkstERGA4tVlgtfGlVXEgFRDSnXtIn/eKBJUiqXTsrI75IT0pypQms2D731 oP971zwgIdG765RA= X-Received: by 2002:a1c:5448:: with SMTP id p8mr3381228wmi.173.1588686962349; Tue, 05 May 2020 06:56:02 -0700 (PDT) X-Google-Smtp-Source: APiQypKPG2+9WRhWYvVyd6+cVVkzlJpqzM/DeMz9N0fQiTyhE729YudHI0TEuEeDZJrelmcOZzK1Dg== X-Received: by 2002:a1c:5448:: with SMTP id p8mr3381193wmi.173.1588686962125; Tue, 05 May 2020 06:56:02 -0700 (PDT) Received: from [192.168.1.38] (26.red-88-21-207.staticip.rima-tde.net. [88.21.207.26]) by smtp.gmail.com with ESMTPSA id f63sm3863626wma.47.2020.05.05.06.56.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 May 2020 06:56:01 -0700 (PDT) Subject: Re: [PATCH 0/4] Add support for SafeStack To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= References: <20200429194420.21147-1-dbuono@linux.vnet.ibm.com> <51f28cf2-0f34-508f-96f8-02c02b3c8a85@redhat.com> <20200505133111.GM764268@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Tue, 5 May 2020 15:56:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200505133111.GM764268@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.81; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/05 00:37:19 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Tobin Feldman-Fitzthum , qemu-devel@nongnu.org, Stefan Hajnoczi , Paolo Bonzini , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Daniele Buono Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/5/20 3:31 PM, Daniel P. Berrang=C3=A9 wrote: > On Tue, May 05, 2020 at 03:15:18PM +0200, Philippe Mathieu-Daud=C3=A9 wro= te: >> +Alex & Daniel who keep track on CI stuff. >> >> On 4/29/20 9:44 PM, Daniele Buono wrote: >>> LLVM supports SafeStack instrumentation to protect against stack buffer >>> overflows, since version 3.7 >>> >>> From https://clang.llvm.org/docs/SafeStack.html: >>> "It works by separating the program stack into two distinct regions: th= e >>> safe stack and the unsafe stack. The safe stack stores return addresses= , >>> register spills, and local variables that are always accessed in a safe >>> way, while the unsafe stack stores everything else. This separation >>> ensures that buffer overflows on the unsafe stack cannot be used to >>> overwrite anything on the safe stack." >>> >>> Unfortunately, the use of two stack regions does not cope well with >>> QEMU's coroutines. The second stack region is not properly set up with >>> both ucontext and sigaltstack, so multiple coroutines end up sharing th= e >>> same memory area for the unsafe stack, causing undefined behaviors at >>> runtime (and most iochecks to fail). >>> >>> This patch series fixes the implementation of the ucontext backend and >>> make sure that sigaltstack is never used if the compiler is applying >>> the SafeStack instrumentation. It also adds a configure flag to enable >>> SafeStack, and enables iotests when SafeStack is used. >>> >>> This is an RFC mainly because of the low-level use of the SafeStack >>> runtime. >>> When running swapcontext(), we have to manually set the unsafe stack >>> pointer to the new area allocated for the coroutine. LLVM does not allo= w >>> this by using builtin, so we have to use implementation details that ma= y >>> change in the future. >>> This patch has been tested briefly ( make check on an x86 system ) with >>> clang v3.9, v4.0, v5.0, v6.0 >>> Heavier testing, with make check-acceptance has been performed with >>> clang v7.0 >> >> I noticed building using SafeStack is slower, and running with it is eve= n >> sloooower. It makes sense to have this integrated if we use it regularly= . Do >> you have plan for this? Using public CI doesn't seem reasonable. >=20 > The runtime behaviour is rather odd, given the docs they provide: >=20 > "The performance overhead of the SafeStack instrumentation is > less than 0.1% on average across a variety of benchmarks > This is mainly because most small functions do not have any > variables that require the unsafe stack and, hence, do not > need unsafe stack frames to be created. The cost of creating > unsafe stack frames for large functions is amortized by the > cost of executing the function. >=20 > In some cases, SafeStack actually improves the performance" I'm sorry I was testing this with a single core instead of all of=20 them... Thanks for looking at the doc. >=20 > Regards, > Daniel >=20