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, 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 9E59FC2D0A3 for ; Wed, 4 Nov 2020 14:41:47 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id A7DD120739 for ; Wed, 4 Nov 2020 14:41:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7DD120739 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-20356-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 31791 invoked by uid 550); 4 Nov 2020 14:41:40 -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 31769 invoked from network); 4 Nov 2020 14:41:39 -0000 Date: Wed, 4 Nov 2020 14:41:21 +0000 From: Catalin Marinas To: Szabolcs Nagy Cc: Jeremy Linton , Mark Brown , libc-alpha@sourceware.org, Mark Rutland , Will Deacon , Florian Weimer , Kees Cook , Salvatore Mesoraca , Lennart Poettering , Topi Miettinen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel-hardening@lists.openwall.com, linux-hardening@vger.kernel.org Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831] Message-ID: <20201104144120.GD28902@gaia> References: <20201103173438.GD5545@sirena.org.uk> <8c99cc8e-41af-d066-b786-53ac13c2af8a@arm.com> <20201104085704.GB24704@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201104085704.GB24704@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) On Wed, Nov 04, 2020 at 08:57:05AM +0000, Szabolcs Nagy wrote: > The 11/03/2020 23:41, Jeremy Linton wrote: > > On 11/3/20 11:34 AM, Mark Brown wrote: > > > On Tue, Nov 03, 2020 at 10:25:37AM +0000, Szabolcs Nagy wrote: > > > > > > > Re-mmap executable segments instead of mprotecting them in > > > > case mprotect is seccomp filtered. > > > > > > > For the kernel mapped main executable we don't have the fd > > > > for re-mmap so linux needs to be updated to add BTI. (In the > > > > presence of seccomp filters for mprotect(PROT_EXEC) the libc > > > > cannot change BTI protection at runtime based on user space > > > > policy so it is better if the kernel maps BTI compatible > > > > binaries with PROT_BTI by default.) > > > > > > Given that there were still some ongoing discussions on a more robust > > > kernel interface here and there seem to be a few concerns with this > > > series should we perhaps just take a step back and disable this seccomp > > > filter in systemd on arm64, at least for the time being? That seems > > > safer than rolling out things that set ABI quickly, a big part of the > > > > So, that's a bigger hammer than I think is needed and punishes !BTI > > machines. I'm going to suggest that if we need to carry a temp patch its > > more like the glibc patch I mentioned in the Fedora defect. That patch > > simply logs a message, on the mprotect failures rather than aborting. Its > > fairly non-intrusive. > > > > That leaves seccomp functional, and BTI generally functional except when > > seccomp is restricting it. I've also been asked that if a patch like that is > > needed, its (temporary?) merged to the glibc trunk, rather than just being > > carried by the distro's. > > note that changing mprotect into mmap in glibc works > even if the kernel or systemd decides to do things > differently: currently the only wart is that on the > main exe we have to use mprotect and silently ignore > the failures. Can the dynamic loader mmap() the main exe again while munmap'ing the original one? (sorry if it was already discussed) -- Catalin