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=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 789FFC4363A for ; Thu, 22 Oct 2020 07:55:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 11EE522267 for ; Thu, 22 Oct 2020 07:55:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gBwKfHc0" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2509053AbgJVHzG (ORCPT ); Thu, 22 Oct 2020 03:55:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:50027 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2440530AbgJVHzG (ORCPT ); Thu, 22 Oct 2020 03:55:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603353305; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dB+TM53F+j8wSOxNsUY6W0vGPFUWPodpwEVY3R8KKXE=; b=gBwKfHc0sHLXLKEeYOj52LcQWdfCbIsVfkSCQxW2daPSeeEZuG4NtIRfoE4IUTDEENmwE1 fcOqtPThKUvcb5HICGu1TguK/cUbOh4tuExbzP7ng2N6KbHDXRmnyq4RKK7E13tUFJsnt3 bd2NiPTfjB50oGpWVBfYOipuaaZEFiw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-592-r9hdCvaaN9-l1Ial5DNDIw-1; Thu, 22 Oct 2020 03:54:58 -0400 X-MC-Unique: r9hdCvaaN9-l1Ial5DNDIw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1E65918BE160; Thu, 22 Oct 2020 07:54:57 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-112-100.ams2.redhat.com [10.36.112.100]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 645216EF61; Thu, 22 Oct 2020 07:54:54 +0000 (UTC) From: Florian Weimer To: Lennart Poettering Cc: Jeremy Linton , Mark Rutland , systemd-devel@lists.freedesktop.org, Kees Cook , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Mark Brown , libc-alpha@sourceware.org, Dave Martin , "linux-arm-kernel@lists.infradead.org" Subject: Re: [systemd-devel] BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures References: <8584c14f-5c28-9d70-c054-7c78127d84ea@arm.com> <20201022071812.GA324655@gardel-login> Date: Thu, 22 Oct 2020 09:54:52 +0200 In-Reply-To: <20201022071812.GA324655@gardel-login> (Lennart Poettering's message of "Thu, 22 Oct 2020 09:18:12 +0200") Message-ID: <87sga6snjn.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Lennart Poettering: > On Mi, 21.10.20 22:44, Jeremy Linton (jeremy.linton@arm.com) wrote: > >> Hi, >> >> There is a problem with glibc+systemd on BTI enabled systems. Systemd >> has a service flag "MemoryDenyWriteExecute" which uses seccomp to deny >> PROT_EXEC changes. Glibc enables BTI only on segments which are marked as >> being BTI compatible by calling mprotect PROT_EXEC|PROT_BTI. That call is >> caught by the seccomp filter, resulting in service failures. >> >> So, at the moment one has to pick either denying PROT_EXEC changes, or BTI. >> This is obviously not desirable. >> >> Various changes have been suggested, replacing the mprotect with mmap calls >> having PROT_BTI set on the original mapping, re-mmapping the segments, >> implying PROT_EXEC on mprotect PROT_BTI calls when VM_EXEC is already set, >> and various modification to seccomp to allow particular mprotect cases to >> bypass the filters. In each case there seems to be an undesirable attribute >> to the solution. >> >> So, whats the best solution? > > Did you see Topi's comments on the systemd issue? > > https://github.com/systemd/systemd/issues/17368#issuecomment-710485532 > > I think I agree with this: it's a bit weird to alter the bits after > the fact. Can't glibc set up everything right from the begining? That > would keep both concepts working. The dynamic loader has to process the LOAD segments to get to the ELF note that says to enable BTI. Maybe we could do a first pass and load only the segments that cover notes. But that requires lots of changes to generic code in the loader. Thanks, Florian -- Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill