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 29554384387A for ; Wed, 11 May 2022 18:22:23 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 29554384387A 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-584-eFby-_7gPDW-l3CASfFxLQ-1; Wed, 11 May 2022 14:22:19 -0400 X-MC-Unique: eFby-_7gPDW-l3CASfFxLQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6461C8032EA; Wed, 11 May 2022 18:22:19 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.194]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8BEE81121314; Wed, 11 May 2022 18:22:18 +0000 (UTC) From: Florian Weimer To: "H.J. Lu" Cc: "H.J. Lu via Gcc-patches" Subject: Re: [PATCH] x86: Document -mno-cet-switch References: <20220510162049.2686945-1-hjl.tools@gmail.com> <87sfpgij2x.fsf@oldenburg.str.redhat.com> <87a6bof4cz.fsf@oldenburg.str.redhat.com> Date: Wed, 11 May 2022 20:22:16 +0200 In-Reply-To: (H. J. Lu's message of "Wed, 11 May 2022 11:00:54 -0700") Message-ID: <87sfpgc4kn.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 2.78 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-5.1 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=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) 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: Wed, 11 May 2022 18:22:24 -0000 * H. J. Lu: >> >> > Generate jump tables with ENDBR and skip the NOTRACK prefix for indirect >> >> > jump. Document -mno-cet-switch to turn off CET instrumentation on jump >> >> > tables for switch statements. >> >> >> >> Of course, that is a slight regression in security hardening. >> >> >> >> Quite frankly, I'm puzzled why the kernel decided to require these >> >> additional ENDBR instructions. >> > >> > Kernel is using -mcet-switch today. Should we document -mcet-switch >> > and keep it off by default instead? >> >> Sorry, I'm not 100% certain of the mechanics/options involved. >> >> I think the default should reflect userspace requirements, like with the >> red zone and vector register usage for integer code. > > The question is if the compiler should use NOTRACK by default for > the jump table. It is independent of whether NOTRACK is enabled or > not. NOTRACK avoids the need for ENDBR instructions, right? That's a hardening improvement, so it should be used by default. Thanks, Florian