From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EAC25C433E6 for ; Fri, 28 Aug 2020 10:21:34 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 4B7B3205CB for ; Fri, 28 Aug 2020 10:21:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4B7B3205CB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19710-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 10180 invoked by uid 550); 28 Aug 2020 10:21:26 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 10160 invoked from network); 28 Aug 2020 10:21:25 -0000 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Date: Fri, 28 Aug 2020 12:21:13 +0200 (CEST) From: Miroslav Benes To: Kristen Carlson Accardi cc: Josh Poimboeuf , Kees Cook , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, arjan@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, rick.p.edgecombe@intel.com, live-patching@vger.kernel.org, Hongjiu Lu , joe.lawrence@redhat.com Subject: Re: [PATCH v4 00/10] Function Granular KASLR In-Reply-To: <46c49dec078cb8625a9c3a3cd1310a4de7ec760b.camel@linux.intel.com> Message-ID: References: <20200717170008.5949-1-kristen@linux.intel.com> <202007220738.72F26D2480@keescook> <20200722160730.cfhcj4eisglnzolr@treble> <202007221241.EBC2215A@keescook> <301c7fb7d22ad6ef97856b421873e32c2239d412.camel@linux.intel.com> <20200722213313.aetl3h5rkub6ktmw@treble> <46c49dec078cb8625a9c3a3cd1310a4de7ec760b.camel@linux.intel.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Leaving Josh's proposals here for reference... > > I'm not sure how LTO does it, but a few more (half-brained) ideas > > that > > could work: > > > > 1) Add a field in kallsyms to keep track of a symbol's original > > offset > > before randomization/re-sorting. Livepatch could use that field > > to > > determine the original sympos. > > > > 2) In fgkaslr code, go through all the sections and mark the ones > > which > > have duplicates (i.e. same name). Then when shuffling the > > sections, > > skip a shuffle if it involves a duplicate section. That way all > > the > > duplicates would retain their original sympos. > > > > 3) Livepatch could uniquely identify symbols by some feature other > > than > > sympos. For example: > > > > Symbol/function size - obviously this would only work if > > duplicately > > named symbols have different sizes. > > > > Checksum - as part of a separate feature we're also looking at > > giving > > each function its own checksum, calculated based on its > > instruction > > opcodes. Though calculating checksums at runtime could be > > complicated by IP-relative addressing. > > > > I'm thinking #1 or #2 wouldn't be too bad. #3 might be harder. > > > > Hi there! I was trying to find a super easy way to address this, so I > thought the best thing would be if there were a compiler or linker > switch to just eliminate any duplicate symbols at compile time for > vmlinux. I filed this question on the binutils bugzilla looking to see > if there were existing flags that might do this, but H.J. Lu went ahead > and created a new one "-z unique", that seems to do what we would need > it to do. > > https://sourceware.org/bugzilla/show_bug.cgi?id=26391 > > When I use this option, it renames any duplicate symbols with an > extension - for example duplicatefunc.1 or duplicatefunc.2. You could > either match on the full unique name of the specific binary you are > trying to patch, or you match the base name and use the extension to > determine original position. Do you think this solution would work? Yes, I think so (thanks, Joe, for testing!). It looks cleaner to me than the options above, but it may just be a matter of taste. Anyway, I'd go with full name matching, because -z unique-symbol would allow us to remove sympos altogether, which is appealing. > If > so, I can modify livepatch to refuse to patch on duplicated symbols if > CONFIG_FG_KASLR and when this option is merged into the tool chain I > can add it to KBUILD_LDFLAGS when CONFIG_FG_KASLR and livepatching > should work in all cases. Ok. Josh, Petr, would this work for you too? Thanks Miroslav