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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 5550AE95A8E for ; Mon, 9 Oct 2023 11:06:32 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qpo5P-0004f9-Fc; Mon, 09 Oct 2023 07:06:07 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qpo5G-0004TP-US for qemu-devel@nongnu.org; Mon, 09 Oct 2023 07:06:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qpo5E-0004B3-UC for qemu-devel@nongnu.org; Mon, 09 Oct 2023 07:05:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1696849555; h=from:from:reply-to: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=fKQvoBSggeAo9XJT7o6oL1AWxeIj3PaIF5ao9fRX0ak=; b=OtP3OmEj9FXwSVEht6Nq2b9ejiexi4MbuKA40nH4asQ7r7vJlPtO70mMfm+9gtYBDQAEfp ziG1VlXKK14w9SPSgKTNqBMJQ2UKxVrBvuVzPbUu+x0p63WtO3h3dOJmXwaz2ZgIEUXBUb k9Ev7pTciruO7453jLcqV3oZD1Gq+9A= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-178-eD3LVn9NNL2bKfjRm5mnEQ-1; Mon, 09 Oct 2023 07:05:42 -0400 X-MC-Unique: eD3LVn9NNL2bKfjRm5mnEQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 00C3681B13F; Mon, 9 Oct 2023 11:05:41 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.42]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B7640170E9; Mon, 9 Oct 2023 11:05:39 +0000 (UTC) Date: Mon, 9 Oct 2023 12:05:37 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Cc: qemu-devel@nongnu.org, Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH 2/2] meson: mitigate against use of uninitialize stack for exploits Message-ID: References: <20231005173812.966264-1-berrange@redhat.com> <20231005173812.966264-3-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Oct 09, 2023 at 12:15:17PM +0200, Thomas Huth wrote: > On 09/10/2023 09.44, Thomas Huth wrote: > > On 05/10/2023 19.38, Daniel P. Berrangé wrote: > > > When variables are used without being initialized, there is potential > > > to take advantage of data that was pre-existing on the stack from an > > > earlier call, to drive an exploit. > > > > > > It is good practice to always initialize variables, and the compiler > > > can warn about flaws when -Wuninitialized is present. This warning, > > > however, is by no means foolproof with its output varying depending > > > on compiler version and which optimizations are enabled. > > > > > > The -ftrivial-auto-var-init option can be used to tell the compiler > > > to always initialize all variables. This increases the security and > > > predictability of the program, closing off certain attack vectors, > > > reducing the risk of unsafe memory disclosure. > > > > > > While the option takes several possible values, using 'zero' is > > > considered to be the  option that is likely to lead to semantically > > > correct or safe behaviour[1]. eg sizes/indexes are not likely to > > > lead to out-of-bounds accesses when initialized to zero. Pointers > > > are less likely to point something useful if initialized to zero. > > > > > > Even with -ftrivial-auto-var-init=zero set, GCC will still issue > ... > > > +    '-ftrivial-var-auto-init=zero', > > >   ] > > There is something fishy here: In the commit description, you write about > "-ftrivial-auto-var-init" but in the code you use "-ftrivial-var-auto-init" > ... that looks wrong to me, please fix! Face palm, -ftrivial-auto-var-init is the correct one. > > I was a little bit torn about using =zero when I first read your patch, > > but after looking at [1], I tend now also tend to agree that =zero is > > likely the best choice. > > Thinking about this twice: What about using -ftrivial-var-auto-init=pattern > for --enable-debug builds, and only use the "zero" init for non-debug > builds? ... that would prevent that people blindly rely on this "language > extension". We can't blindly rely on it, because -Wuninitialized is still going to do static analysis and warn in most cases, which can't be ignored when -Werror is set. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|