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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 B0890C43331 for ; Wed, 25 Mar 2020 12:24:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8055B2078A for ; Wed, 25 Mar 2020 12:24:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727046AbgCYMY5 (ORCPT ); Wed, 25 Mar 2020 08:24:57 -0400 Received: from foss.arm.com ([217.140.110.172]:47652 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726998AbgCYMY4 (ORCPT ); Wed, 25 Mar 2020 08:24:56 -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 1188731B; Wed, 25 Mar 2020 05:24:56 -0700 (PDT) Received: from [192.168.1.123] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C816F3F71F; Wed, 25 Mar 2020 05:24:54 -0700 (PDT) Subject: Re: [PATCH 0/3] arm64: Open code .arch_extension To: Mark Rutland , Ard Biesheuvel Cc: Eric Biggers , Catalin Marinas , Mark Brown , linux-crypto@vger.kernel.org, Will Deacon , linux-arm-kernel@lists.infradead.org References: <20200325114110.23491-1-broonie@kernel.org> <20200325115038.GD4346@sirena.org.uk> <20200325120224.GA34330@C02TD0UTHF1T.local> From: Robin Murphy Message-ID: Date: Wed, 25 Mar 2020 12:24:53 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200325120224.GA34330@C02TD0UTHF1T.local> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-crypto-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org On 2020-03-25 12:03 pm, Mark Rutland wrote: > On Wed, Mar 25, 2020 at 12:54:10PM +0100, Ard Biesheuvel wrote: >> On Wed, 25 Mar 2020 at 12:50, Mark Brown wrote: >>> Since BTI is a mandatory feature of v8.5 there is no BTI arch_extension, >>> you can only enable it by moving the base architecture to v8.5. You'd >>> need to use .arch and that feels likely to find us sharp edges to run >>> into. >> >> I think we should talk to the toolchain folks about this. Even if >> .arch_extension today does not support the 'bti' argument, it *is* >> most definitely an architecture extension, even it it is mandatory in >> v8.5 (given that v8.5 is itself an architecture extension). > > It certianly seems unfortunate, as it goes against the premise of having > HINT space instructions. Most software will want to enable HINT space > instructions from ARMv8.x but nothing else to ensure binary > compatibility with existing hardware. > > I see the same is true for pointer authentication judging by: > > https://sourceware.org/binutils/docs/as/AArch64-Extensions.html#AArch64-Extensions > > ... so worth raising with toolchain folk as a general principle even if > we have to bodge around it for now. Indeed, in general, just because a feature is mandatory in v8.n doesn't necessarily mean it can't be included in a v8.(n-1) implementation which may not have the *other* mandatory parts of v8.n which ".arch armv8.-a" would let through. Robin.