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 21134C46CD2 for ; Tue, 9 Jan 2024 14:54:39 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rNDUo-0002fj-0U; Tue, 09 Jan 2024 09:54:27 -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 1rNDUd-0002Y3-Ed for qemu-devel@nongnu.org; Tue, 09 Jan 2024 09:54:15 -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 1rNDUb-0005Pz-F5 for qemu-devel@nongnu.org; Tue, 09 Jan 2024 09:54:15 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704812052; 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=qT5StO/GePljQeQo4FtH1LtnBaFd+lBt2tcpU1tcwnI=; b=UKI8FZ351II4AIIzb/jLF34uc9qhfL0TLptiCgO2EHhqZs8BpswIPWd3+i3cjhjX1ovy3A ve6P0rxHNU/6D2dfm4tqn3Y7UzNg8kZB8InfZp/cWiu1GjoODi/S6hzqIByANUuyweXM+3 6zrt/hTFNG6JsfWkbMZ6hdeMVVnUY1Q= 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-548-veKShO4vMj2rFB8sK_uupQ-1; Tue, 09 Jan 2024 09:54:09 -0500 X-MC-Unique: veKShO4vMj2rFB8sK_uupQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (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 00ED983DDE5; Tue, 9 Jan 2024 14:54:09 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.71]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BA79F2026D6F; Tue, 9 Jan 2024 14:54:08 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id BA27421E680D; Tue, 9 Jan 2024 15:54:07 +0100 (CET) From: Markus Armbruster To: Daniel P. =?utf-8?Q?Berrang=C3=A9?= 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 1/2] meson: mitigate against ROP exploits with -fzero-call-used-regs In-Reply-To: <20240103123414.2401208-2-berrange@redhat.com> ("Daniel P. =?utf-8?Q?Berrang=C3=A9=22's?= message of "Wed, 3 Jan 2024 12:34:13 +0000") References: <20240103123414.2401208-1-berrange@redhat.com> <20240103123414.2401208-2-berrange@redhat.com> Date: Tue, 09 Jan 2024 15:54:07 +0100 Message-ID: <87bk9ulfqo.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Daniel P. Berrang=C3=A9 writes: > To quote wikipedia: > > "Return-oriented programming (ROP) is a computer security exploit > technique that allows an attacker to execute code in the presence > of security defenses such as executable space protection and code > signing. > > In this technique, an attacker gains control of the call stack to > hijack program control flow and then executes carefully chosen > machine instruction sequences that are already present in the > machine's memory, called "gadgets". Each gadget typically ends in > a return instruction and is located in a subroutine within the > existing program and/or shared library code. Chained together, > these gadgets allow an attacker to perform arbitrary operations > on a machine employing defenses that thwart simpler attacks." > > QEMU is by no means perfect with an ever growing set of CVEs from > flawed hardware device emulation, which could potentially be > exploited using ROP techniques. > > Since GCC 11 there has been a compiler option that can mitigate > against this exploit technique: > > -fzero-call-user-regs > > To understand it refer to these two resources: > > https://www.jerkeby.se/newsletter/posts/rop-reduction-zero-call-user-r= egs/ > https://gcc.gnu.org/pipermail/gcc-patches/2020-August/552262.html > > I used two programs to scan qemu-system-x86_64 for ROP gadgets: > > https://github.com/0vercl0k/rp > https://github.com/JonathanSalwan/ROPgadget > > When asked to find 8 byte gadgets, the 'rp' tool reports: > > A total of 440278 gadgets found. > You decided to keep only the unique ones, 156143 unique gadgets found. > > While the ROPgadget tool reports: > > Unique gadgets found: 353122 > > With the --ropchain argument, the latter attempts to use the found > gadgets to product a chain that can execute arbitrary syscalls. With > current QEMU it succeeds in this task, which is an undesirable > situation. > > With QEMU modified to use -fzero-call-user-regs=3Dused-gpr the 'rp' tool > reports > > A total of 528991 gadgets found. > You decided to keep only the unique ones, 121128 unique gadgets found. > > This is 22% fewer unique gadgets > > While the ROPgadget tool reports: > > Unique gadgets found: 328605 > > This is 7% fewer unique gadgets. Crucially though, despite this more > modest reduction, the ROPgadget tool is no longer able to identify a > chain of gadgets for executing arbitrary syscalls. It fails at the > very first step, unable to find gadgets for populating registers for > a future syscall. Having said that, more advanced tools do still > manage to put together a viable ROP chain. > > Also this only takes into account QEMU code. QEMU links to many 3rd > party shared libraries and ideally all of them would be compiled with > this same hardening. That becomes a distro policy question though. > > In terms of performance impact, TCG was used as an evaluation test > case. We're not interested in protecting TCG since it isn't designed > to provide a security barrier, but it is performance sensitive code, > so useful as a guide to how other areas of QEMU might be impacted. > With the -fzero-call-user-regs=3Dused-gpr argument present, using the > real world test of booting a linux kernel and having init immediately > poweroff, there is a ~1% slow down in performance under TCG. The QEMU > binary size also grows by approximately 1%. > > By comparison, using the more aggressive -fzero-call-user-regs=3Dall, > results in a slowdown of over 25% in TCG, which is clearly not an > acceptable impact, and a binary size increase of 5%. > > Considering that 'used-gpr' succesfully stopped ROPgadget assembling > a chain, this more targetted protection is a justifiable hardening > / performance tradeoff. Have you also considered 'used-arg'? > Reviewed-by: Thomas Huth > Signed-off-by: Daniel P. Berrang=C3=A9 > --- > meson.build | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/meson.build b/meson.build > index 6c77d9687d..eaa20d241d 100644 > --- a/meson.build > +++ b/meson.build > @@ -433,6 +433,17 @@ if get_option('fuzzing') > endif > endif >=20=20 > +# Check further flags that make QEMU more robust against malicious parti= es > + > +hardening_flags =3D [ > + # Zero out registers used during a function call > + # upon its return. This makes it harder to assemble > + # ROP gadgets into something usable > + '-fzero-call-used-regs=3Dused-gpr', > +] > + > +qemu_common_flags +=3D cc.get_supported_arguments(hardening_flags) > + > add_global_arguments(qemu_common_flags, native: false, language: all_lan= guages) > add_global_link_arguments(qemu_ldflags, native: false, language: all_lan= guages)