From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_PASS autolearn=ham autolearn_force=no version=3.4.2 Received: (qmail 12512 invoked from network); 21 Apr 2020 09:57:20 -0000 Received-SPF: pass (mother.openwall.net: domain of lists.openwall.com designates 195.42.179.200 as permitted sender) receiver=inbox.vuxu.org; client-ip=195.42.179.200 envelope-from= Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with UTF8ESMTPZ; 21 Apr 2020 09:57:20 -0000 Received: (qmail 16318 invoked by uid 550); 21 Apr 2020 09:57:18 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 16300 invoked from network); 21 Apr 2020 09:57:18 -0000 From: Florian Weimer To: Nicholas Piggin Cc: Rich Felker , Nicholas Piggin via Libc-alpha , libc-dev@lists.llvm.org, linuxppc-dev@lists.ozlabs.org, musl@lists.openwall.com References: <1586931450.ub4c8cq8dj.astroid@bobo.none> <20200415225539.GL11469@brightrain.aerifal.cx> <1586994952.nnxigedbu2.astroid@bobo.none> <20200416095800.GC23945@port70.net> <1587341904.1r83vbudyf.astroid@bobo.none> <20200420012904.GY11469@brightrain.aerifal.cx> <1587348046.pwnfbo52iq.astroid@bobo.none> <20200420211751.GF23945@port70.net> Date: Tue, 21 Apr 2020 11:57:00 +0200 In-Reply-To: <20200420211751.GF23945@port70.net> (Szabolcs Nagy's message of "Mon, 20 Apr 2020 23:17:51 +0200") Message-ID: <87eeshupoz.fsf@mid.deneb.enyo.de> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [musl] Powerpc Linux 'scv' system call ABI proposal take 2 * Szabolcs Nagy: > * Nicholas Piggin [2020-04-20 12:08:36 +1000]: >> Excerpts from Rich Felker's message of April 20, 2020 11:29 am: >> > Also, allowing patching of executable pages is generally frowned upon >> > these days because W^X is a desirable hardening property. >> >> Right, it would want be write-protected after being patched. > > "frowned upon" means that users may have to update > their security policy setting in pax, selinux, apparmor, > seccomp bpf filters and who knows what else that may > monitor and flag W&X mprotect. > > libc update can break systems if the new libc does W&X. It's possible to map over pre-compiled alternative implementations, though. Basically, we would do the patching and build time and store the results in the file. It works best if the variance is concentrated on a few pages, and there are very few alternatives. For example, having two syscall APIs and supporting threading and no-threading versions would need four code versions in total, which is likely excessive.