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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 9D0D7C2D0A3 for ; Wed, 4 Nov 2020 05:41:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AB89206FB for ; Wed, 4 Nov 2020 05:41:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728221AbgKDFlp (ORCPT ); Wed, 4 Nov 2020 00:41:45 -0500 Received: from foss.arm.com ([217.140.110.172]:60192 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725535AbgKDFlp (ORCPT ); Wed, 4 Nov 2020 00:41:45 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E15A71474; Tue, 3 Nov 2020 21:41:43 -0800 (PST) Received: from [192.168.122.166] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 61DE03F719; Tue, 3 Nov 2020 21:41:43 -0800 (PST) Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831] To: Mark Brown , Szabolcs Nagy Cc: libc-alpha@sourceware.org, Catalin Marinas , 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 References: <20201103173438.GD5545@sirena.org.uk> From: Jeremy Linton Message-ID: <8c99cc8e-41af-d066-b786-53ac13c2af8a@arm.com> Date: Tue, 3 Nov 2020 23:41:42 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201103173438.GD5545@sirena.org.uk> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, 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. Thanks, > reason we went with having the dynamic linker enable PROT_BTI in the > first place was to give us more flexibility to handle any unforseen > consequences of enabling BTI that we run into. We are going to have > similar issues with other features like MTE so we need to make sure that > whatever we're doing works with them too. > > Also updated to Will's current e-mail address - Will, do you have > thoughts on what we should do here? >