From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 88C9C3839C46 for ; Thu, 19 May 2022 20:49:17 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 88C9C3839C46 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-416-AVjKNqLVNHKPadmqP7idcA-1; Thu, 19 May 2022 16:49:15 -0400 X-MC-Unique: AVjKNqLVNHKPadmqP7idcA-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B12BC29AA2F0; Thu, 19 May 2022 20:49:14 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.58]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B17FFC159B3; Thu, 19 May 2022 20:49:13 +0000 (UTC) From: Florian Weimer To: "H.J. Lu" Cc: Richard Biener , GCC Patches Subject: Re: [PATCH v2] x86: Document -mcet-switch References: <20220511205251.2947362-1-hjl.tools@gmail.com> Date: Thu, 19 May 2022 22:49:11 +0200 In-Reply-To: (H. J. Lu's message of "Thu, 19 May 2022 13:37:10 -0700") Message-ID: <87fsl5w8mw.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-5.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 19 May 2022 20:49:19 -0000 * H. J. Lu: > How about this? > > @item -mcet-switch > @opindex mcet-switch > By default, CET instrumentation is turned off on switch statements that > use a jump table and indirect branch track is disabled. Maybe add here: =E2=80=9CSince jump tables are stored in read-only memory, = this does not result in a direct loss of hardening. But if the jump table index is attacker-controlled, the indirect jump may not be constrained by CET.=E2=80=9D > This option turns on CET instrumentation to enable indirect branch > track for switch statements with jump tables. =E2=80=9CThis results in a loss of hardening because the jump targets are m= ow reachable via all indirect jumps.=E2=80=9D Maybe GCC should just emit a forced (unoptimized) bounds check for jump tables in CET mode =E2=80=A6 Thanks, Florian