From patchwork Wed Jan 3 12:34:14 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= X-Patchwork-Id: 13509976 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 2FF69C3DA6E for ; Wed, 3 Jan 2024 12:35:21 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rL0S5-0000sP-9Y; Wed, 03 Jan 2024 07:34:29 -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 1rL0Rz-0000qz-8V for qemu-devel@nongnu.org; Wed, 03 Jan 2024 07:34:23 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rL0Rw-0003uE-AK for qemu-devel@nongnu.org; Wed, 03 Jan 2024 07:34:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704285259; 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=nrFKz8BYhYwNgk4nJMheNQQMLEAcYlF6sVVqRUnrJg0=; b=KEtxdVmOsc4gP3cl8dLfZKd2KDi4bOz5YuyBEqDdNgHqB2w/g1CtqKTuXUk/YSuBal87ST MPXxDa6uVrydMFBm9PKcTbkFKnyrbrM0mcKzP5q7XzK7ft+uqgh33GoLVM12OsLSMBbkcZ New+7gohJ5DhGP47Ec0AdlZPC3h0HbM= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-479-FR20wc7CNL2ZAWyMNBg2hA-1; Wed, 03 Jan 2024 07:34:18 -0500 X-MC-Unique: FR20wc7CNL2ZAWyMNBg2hA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (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 074D91C05135; Wed, 3 Jan 2024 12:34:18 +0000 (UTC) Received: from toolbox.redhat.com (unknown [10.42.28.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1B73840C6EB9; Wed, 3 Jan 2024 12:34:17 +0000 (UTC) From: =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= To: qemu-devel@nongnu.org Cc: Thomas Huth , Paolo Bonzini , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , =?utf-8?q?Phil?= =?utf-8?q?ippe_Mathieu-Daud=C3=A9?= , =?utf-8?q?Marc-And?= =?utf-8?q?r=C3=A9_Lureau?= Subject: [PATCH v2 2/2] meson: mitigate against use of uninitialize stack for exploits Date: Wed, 3 Jan 2024 12:34:14 +0000 Message-ID: <20240103123414.2401208-3-berrange@redhat.com> In-Reply-To: <20240103123414.2401208-1-berrange@redhat.com> References: <20240103123414.2401208-1-berrange@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -46 X-Spam_score: -4.7 X-Spam_bar: ---- X-Spam_report: (-4.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.601, 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_H4=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 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)