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 CD579C47077 for ; Tue, 9 Jan 2024 14:54:01 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rNDUK-0001mp-1p; Tue, 09 Jan 2024 09:53:56 -0500 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 1rNDUI-0001fM-5R for qemu-devel@nongnu.org; Tue, 09 Jan 2024 09:53:54 -0500 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 1rNDUG-0005M7-5K for qemu-devel@nongnu.org; Tue, 09 Jan 2024 09:53:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704812030; 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=bmU/KtFRTRolPp7GSwCCVmfM1nXQCGKQ4dFu+06tdNQ=; b=gTmK+rbYB+V0+ZfWLwlWhL2Q5Ia+ZQ3tPfJvObyzW/B0DYVzrglBja88y2Bkn9A6JLVefC +31I3YLb9ByRGNL4a9VNjwA8TbHNS6KMhh/mLOiAL7muv20CmfWUUXMvKIzMGWs21FaLVl xzG36vNNYqqq2uvOX+bLxQVdAylAItM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-584-_1nHUnGsO-CY4M_A99Nbdg-1; Tue, 09 Jan 2024 09:53:47 -0500 X-MC-Unique: _1nHUnGsO-CY4M_A99Nbdg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 53892811E9C; Tue, 9 Jan 2024 14:53:47 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.86]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 44EF351E3; Tue, 9 Jan 2024 14:53:46 +0000 (UTC) Date: Tue, 9 Jan 2024 14:53:43 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: qemu-devel@nongnu.org, Thomas Huth , Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [PATCH v2 2/2] meson: mitigate against use of uninitialize stack for exploits Message-ID: References: <20240103123414.2401208-1-berrange@redhat.com> <20240103123414.2401208-3-berrange@redhat.com> <87frz6lfzp.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87frz6lfzp.fsf@pond.sub.org> User-Agent: Mutt/2.2.10 (2023-03-25) X-Scanned-By: MIMEDefang 3.4.1 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: -45 X-Spam_score: -4.6 X-Spam_bar: ---- X-Spam_report: (-4.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.493, 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, T_SCC_BODY_TEXT_LINE=-0.01 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 Tue, Jan 09, 2024 at 03:48:42PM +0100, Markus Armbruster wrote: > Daniel P. Berrangé writes: > > > 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 > > warnings with -Wuninitialized if it discovers a problem, so we are > > not loosing diagnostics for developers, just hardening runtime > > behaviour and making QEMU behave more predictably in case of hitting > > bad codepaths. > > > > [1] https://lists.llvm.org/pipermail/cfe-dev/2020-April/065221.html > > Signed-off-by: Daniel P. Berrangé > > --- > > meson.build | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/meson.build b/meson.build > > index eaa20d241d..efc1b4dd14 100644 > > --- a/meson.build > > +++ b/meson.build > > @@ -440,6 +440,11 @@ hardening_flags = [ > > # upon its return. This makes it harder to assemble > > # ROP gadgets into something usable > > '-fzero-call-used-regs=used-gpr', > > + > > + # Initialize all stack variables to zero. This makes > > + # it harder to take advantage of uninitialized stack > > + # data to drive exploits > > + '-ftrivial-auto-var-init=zero', > > ] > > > > qemu_common_flags += cc.get_supported_arguments(hardening_flags) > > Have you tried to throw in -Wtrivial-auto-var-init? > > Documentation, for your convenience: > > ‘-Wtrivial-auto-var-init’ > Warn when ‘-ftrivial-auto-var-init’ cannot initialize the automatic > variable. A common situation is an automatic variable that is > declared between the controlling expression and the first case > label of a ‘switch’ statement. No, I didn't notice that warning. I'll have a look if it reoprts any problems, but not optimistic since we probably have such code patterns. 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 :|