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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 E21D1C3F2CD for ; Mon, 23 Mar 2020 13:24:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B67C62070A for ; Mon, 23 Mar 2020 13:24:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584969856; bh=F0dbBWUdVy6KZJDYW2cN+AHaDgD57xXjJSBoWpC12O4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=eAU58cCWXI/CPNxSZ4FYzcyS1grqRBf+oO+uvRORCiOWQbxu+6NLJ+BAZE1fOHPQC Sy+ptB15dvz/jK7oavH4jbwiR3880uVEm+eu7lZ9lBLbHiZVacCMhPCyawlsmX6klq eQXjgiXNV0O8taaKZRspDb/xcnUswTgNrwClpS8w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728454AbgCWNYP (ORCPT ); Mon, 23 Mar 2020 09:24:15 -0400 Received: from foss.arm.com ([217.140.110.172]:48924 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728344AbgCWNYP (ORCPT ); Mon, 23 Mar 2020 09:24:15 -0400 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 BD6651FB; Mon, 23 Mar 2020 06:24:14 -0700 (PDT) Received: from localhost (unknown [10.37.6.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 403A23F52E; Mon, 23 Mar 2020 06:24:14 -0700 (PDT) Date: Mon, 23 Mar 2020 13:24:12 +0000 From: Mark Brown To: Catalin Marinas Cc: Szabolcs Nagy , Will Deacon , Alexander Viro , Paul Elliott , Peter Zijlstra , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , Marc Zyngier , Eugene Syromiatnikov , "H . J . Lu " , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Thomas Gleixner , Florian Weimer , Sudakshina Das , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, nd@arm.com Subject: Re: [PATCH v10 00/13] arm64: Branch Target Identification support Message-ID: <20200323132412.GD4948@sirena.org.uk> References: <20200316165055.31179-1-broonie@kernel.org> <20200320173945.GC27072@arm.com> <20200323122143.GB4892@mbp> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="n2Pv11Ogg/Ox8ay5" Content-Disposition: inline In-Reply-To: <20200323122143.GB4892@mbp> X-Cookie: Stay on the trail. User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --n2Pv11Ogg/Ox8ay5 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Mon, Mar 23, 2020 at 12:21:44PM +0000, Catalin Marinas wrote: > On Fri, Mar 20, 2020 at 05:39:46PM +0000, Szabolcs Nagy wrote: > +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, > + bool has_interp, bool is_interp) > +{ > + if (is_interp != has_interp) > + return prot; > + > + if (!(state->flags & ARM64_ELF_BTI)) > + return prot; > + > + if (prot & PROT_EXEC) > + prot |= PROT_BTI; > + > + return prot; > +} > At a quick look, for dynamic binaries we have has_interp == true and > is_interp == false. I don't know why but, either way, the above code > needs a comment with some justification. I don't really know for certain either, I inherited this code as is with the understanding that this was all agreed with the toolchain and libc people - the actual discussion that lead to the decisions being made happened before I was involved. My understanding is that the idea was that the dynamic linker would be responsible for mapping everything in dynamic applications other than itself but other than consistency I don't know why. I guess it defers more decision making to userspace but I'm having a hard time thinking of sensible cases where one might wish to make a decision other than enabling PROT_BTI. I'd be perfectly happy to drop the check if that makes more sense to people, otherwise I can send a patch adding a comment explaining the situation. --n2Pv11Ogg/Ox8ay5 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAl54uHwACgkQJNaLcl1U h9DAYQf+PC+yaMtvYW9mN4nKAz7ncHVrReSbAGM8vzqPWdFAlq9YUOWrM19ZtwX3 Reos273yUIeierbiwvJMNq+eDPFo9bF3mqTxkQr5uA4+RDAqXedTNeS637lX1tG3 /uzSb0uqwvff1A9+IZsavz2GuhK8WNmybN7xbOPD1SLHZd4ouEiMlBoE3Ze+nMqm gClUEz9TTAmK6m9sL7rchJgnSFoG5OU4F/6sWpCoip4mFa5QnBAkeWh6RssDImFg hIm9njv6a9aeNHTw1YnM1heqRe86GkmGk3LsgGrHETzDNFOwlBNek95tXIVl7W7I f99IlRUisKUN9wu9VYAtNzRSGiDGLQ== =70MP -----END PGP SIGNATURE----- --n2Pv11Ogg/Ox8ay5--