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 BA79B3858D35 for ; Fri, 14 Jan 2022 13:36:37 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org BA79B3858D35 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-184-eQAah2ufPRiIcSj7ZNrWFg-1; Fri, 14 Jan 2022 08:36:32 -0500 X-MC-Unique: eQAah2ufPRiIcSj7ZNrWFg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 292CA1083F7A; Fri, 14 Jan 2022 13:36:30 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.192.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9E985703B8; Fri, 14 Jan 2022 13:36:26 +0000 (UTC) From: Florian Weimer To: Andy Lutomirski Cc: linux-arch@vger.kernel.org, Linux API , linux-x86_64@vger.kernel.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, the arch/x86 maintainers , musl@lists.openwall.com, libc-alpha@sourceware.org, linux-kernel@vger.kernel.org, Dave Hansen , Kees Cook , Andrei Vagin Subject: Re: [PATCH v3 1/3] x86: Implement arch_prctl(ARCH_VSYSCALL_CONTROL) to disable vsyscall References: <3a1c8280967b491bf6917a18fbff6c9b52e8df24.1641398395.git.fweimer@redhat.com> Date: Fri, 14 Jan 2022 14:36:24 +0100 In-Reply-To: (Andy Lutomirski's message of "Thu, 13 Jan 2022 13:47:26 -0800") Message-ID: <87sftqtp5z.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Spam-Status: No, score=-6.4 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP 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: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 14 Jan 2022 13:36:38 -0000 * Andy Lutomirski: > Is there a reason you didn't just change the check earlier in the > function to: > > if (vsyscall_mode == NONE || current->mm->context.vsyscall_disabled) Andrei requested that I don't print anything if vsyscall was disabled. The original patch used a different message for better diagnostics. > Also, I still think the prctl should not be available if > vsyscall=emulate. Either we should fully implement it or we should > not implement. We could even do: > > pr_warn_once("userspace vsyscall hardening request ignored because you > have vsyscall=emulate. Unless you absolutely need vsyscall=emulate, > update your system to use vsyscall=xonly.\n"); > > and thus encourage good behavior. I think there is still some hardening applied even with vsyscall=emulate. The question is what is more important: the additional hardening, or clean, easily described behavior of the interface. Maybe ARCH_VSYSCALL_CONTROL could return different values based on to what degree it could disable vsyscall? The pr_warn_once does not seem particularly useful. Anyone who upgrades glibc and still uses vsyscall=emulate will see that, with no way to disable it. Thanks, Florian