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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 835C9C3F2CD for ; Mon, 23 Mar 2020 13:57:41 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 37C0320735 for ; Mon, 23 Mar 2020 13:57:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="bq2qEWBj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 37C0320735 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=RDMuintIpd/r9emT11uptFp7Pv8Aih5HtLvYemfGdm0=; b=bq2qEWBj2qI+Fa 41SADjorusSnumeZj0eGQtWqFyiLjiTWuCgKVa1bzURPZI5iZglrcYwuedFa3B8Q9gSUfNXIJ+cys lKw8xz2C3bHXvAiBxerwKUiNo9lg8NwITXHFNitwlwpzJu7bJxt7AhFYAN7HKf4UDTp242N42oel6 Nk4A70rH7rSAtCye3UPfGDCevSSv+RHRc4SU8kTEaTGhfzAsRp9o253w1eA8Tu+uHKlOzGbWUWV9+ ls9ohO45jiyke59izsRN4DFQ3rKDOfPLGRcmZlHM+yKn+NBM+RRk304pHgLRwKq814PrmSOrQqU7j R2qIPHmf7Qv417hj736A==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jGNaE-00065V-Ie; Mon, 23 Mar 2020 13:57:38 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jGNaB-00065B-Bv for linux-arm-kernel@lists.infradead.org; Mon, 23 Mar 2020 13:57:37 +0000 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 271AC1FB; Mon, 23 Mar 2020 06:57:34 -0700 (PDT) Received: from C02TD0UTHF1T.local (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 919783F52E; Mon, 23 Mar 2020 06:57:28 -0700 (PDT) Date: Mon, 23 Mar 2020 13:57:22 +0000 From: Mark Rutland To: Mark Brown Subject: Re: [PATCH v10 00/13] arm64: Branch Target Identification support Message-ID: <20200323135722.GA3959@C02TD0UTHF1T.local> References: <20200316165055.31179-1-broonie@kernel.org> <20200320173945.GC27072@arm.com> <20200323122143.GB4892@mbp> <20200323132412.GD4948@sirena.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200323132412.GD4948@sirena.org.uk> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200323_065735_498050_C40CB770 X-CRM114-Status: GOOD ( 16.90 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paul Elliott , Szabolcs Nagy , Catalin Marinas , Andrew Jones , Amit Kachhap , Vincenzo Frascino , Will Deacon , linux-arch@vger.kernel.org, Marc Zyngier , Eugene Syromiatnikov , Peter Zijlstra , "H . J . Lu " , Yu-cheng Yu , Kees Cook , Arnd Bergmann , Jann Horn , Richard Henderson , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Alexander Viro , Thomas Gleixner , nd@arm.com, linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Sudakshina Das Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Mar 23, 2020 at 01:24:12PM +0000, Mark Brown wrote: > 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. My understanding was this had been agreed with the toolchain folk a while back -- anything static loaded by the kernel (i.e. a static executable or the dynamic linker) would get GP set. In other cases the linker will mess with the permissions on the pages anyhow, and needs to be aware of BTI in order to do the right thing, so it was better to leave it to userspace consistently (e.g. as that had the least risk of subtle changes in behaviour leading to ABI difficulties). > 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. I think it would be best to document the current behaviour, as it's a simple ABI that we can guarantee, and the dynamic linker will have to be aware of BTI in order to do the right thing anyhow. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel