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,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 F3DCFC47096 for ; Thu, 3 Jun 2021 18:05:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7DCC613F4 for ; Thu, 3 Jun 2021 18:05:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230116AbhFCSHW (ORCPT ); Thu, 3 Jun 2021 14:07:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:46236 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230436AbhFCSGz (ORCPT ); Thu, 3 Jun 2021 14:06:55 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CD84D613E3; Thu, 3 Jun 2021 18:04:33 +0000 (UTC) Date: Thu, 3 Jun 2021 19:04:31 +0100 From: Catalin Marinas To: Mark Brown Cc: Dave Martin , Will Deacon , Szabolcs Nagy , Jeremy Linton , "H . J . Lu" , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, libc-alpha@sourceware.org Subject: Re: [PATCH v1 2/2] arm64: Enable BTI for main executable as well as the interpreter Message-ID: <20210603180429.GI20338@arm.com> References: <20210521144621.9306-1-broonie@kernel.org> <20210521144621.9306-3-broonie@kernel.org> <20210603154034.GH4187@arm.com> <20210603165134.GF4257@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210603165134.GF4257@sirena.org.uk> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Thu, Jun 03, 2021 at 05:51:34PM +0100, Mark Brown wrote: > On Thu, Jun 03, 2021 at 04:40:35PM +0100, Dave Martin wrote: > > Do we know how libcs will detect that they don't need to do the > > mprotect() calls? Do we need a detection mechanism at all? > > > > Ignoring certain errors from mprotect() when ld.so is trying to set > > PROT_BTI on the main executable's code pages is probably a reasonable, > > backwards-compatible compromise here, but it seems a bit wasteful. > > I think the theory was that they would just do the mprotect() calls and > ignore any errors as they currently do, or declare that they depend on a > new enough kernel version I guess (not an option for glibc but might be > for others which didn't do BTI yet). I think we discussed the possibility of an AT_FLAGS bit. Until recently, this field was 0 but it gained a new bit now. If we are to expose this to arch-specific things, it may need some reservations. Anyway, that's an optimisation that can be added subsequently. -- Catalin