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=-3.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 57BCFC4363A for ; Thu, 22 Oct 2020 08:25:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF49D223FB for ; Thu, 22 Oct 2020 08:25:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VRpV6lMz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408083AbgJVIZf (ORCPT ); Thu, 22 Oct 2020 04:25:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:23082 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725980AbgJVIZe (ORCPT ); Thu, 22 Oct 2020 04:25:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603355133; 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=SnmBgwDYPdid0KKn11DGxkxXghl8eOjBqUMsY5IBsf0=; b=VRpV6lMzL4uZ9hGHaFURQCQMzj9vP4DvSGyw4bxHH4ABnO7//Jhv6GIoR59ILgHWFsMd+h TZHW+dBFEivxHkUX3Md/mwK/wTbfS705w9u2a6d/Y5v9yJcCi29r2+nNo4d77llBRi9StO Cf+Waxt+jXVTntfR/OWFX/qPPmsYHv0= 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-141-XEJpBZlwP4WaXlKWW9MDSA-1; Thu, 22 Oct 2020 04:25:28 -0400 X-MC-Unique: XEJpBZlwP4WaXlKWW9MDSA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CB711107ACF5; Thu, 22 Oct 2020 08:25:26 +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 DE4535C1C7; Thu, 22 Oct 2020 08:25:23 +0000 (UTC) From: Florian Weimer To: Topi Miettinen Cc: Lennart Poettering , 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> <87sga6snjn.fsf@oldenburg2.str.redhat.com> <511318fd-efde-f2fc-9159-9d16ac8d33a7@gmail.com> Date: Thu, 22 Oct 2020 10:25:22 +0200 In-Reply-To: <511318fd-efde-f2fc-9159-9d16ac8d33a7@gmail.com> (Topi Miettinen's message of "Thu, 22 Oct 2020 11:17:19 +0300") Message-ID: <87d01asm4t.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 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Topi Miettinen: >> 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. > > What if the loader always enabled BTI for PROT_EXEC pages, but then > when discovering that this was a mistake, mprotect() the pages without > BTI? Is that architecturally supported? How costly is the mprotect change if the pages have not been faulted in yet? > Then both BTI and MDWX would work and the penalty of not getting > MDWX would fall to non-BTI programs. What's the expected proportion of > BTI enabled code vs. disabled in the future, is it perhaps expected > that a distro would enable the flag globally so eventually only a few > legacy programs might be unprotected? Eventually, I expect that mainstream distributions build everything for BTI, so yes, the PROT_BTI removal would only be needed for legacy programs. 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