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=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 2EC28C433DF for ; Fri, 9 Oct 2020 10:16:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE04C222B9 for ; Fri, 9 Oct 2020 10:16:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387566AbgJIKQt (ORCPT ); Fri, 9 Oct 2020 06:16:49 -0400 Received: from mail.kernel.org ([198.145.29.99]:40952 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726357AbgJIKQt (ORCPT ); Fri, 9 Oct 2020 06:16:49 -0400 Received: from gaia (unknown [95.149.105.49]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3CB2822276; Fri, 9 Oct 2020 10:16:46 +0000 (UTC) Date: Fri, 9 Oct 2020 11:16:43 +0100 From: Catalin Marinas To: Vincenzo Frascino Cc: Andrey Konovalov , Dmitry Vyukov , kasan-dev@googlegroups.com, Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Elena Petrova , Branislav Rankov , Kevin Brodsky , Will Deacon , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 29/39] arm64: mte: Switch GCR_EL1 in kernel entry and exit Message-ID: <20201009101643.GG23638@gaia> References: <1f2681fdff1aa1096df949cb8634a9be6bf4acc4.1601593784.git.andreyknvl@google.com> <20201002140652.GG7034@gaia> <1b2327ee-5f30-e412-7359-32a7a38b4c8d@arm.com> <20201009081111.GA23638@gaia> <106f8670-3dd0-70ad-91ac-4f419585df50@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <106f8670-3dd0-70ad-91ac-4f419585df50@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 09, 2020 at 10:56:02AM +0100, Vincenzo Frascino wrote: > On 10/9/20 9:11 AM, Catalin Marinas wrote: > > On Thu, Oct 08, 2020 at 07:24:12PM +0100, Vincenzo Frascino wrote: > >> On 10/2/20 3:06 PM, Catalin Marinas wrote: > >>> On Fri, Oct 02, 2020 at 01:10:30AM +0200, Andrey Konovalov wrote: > >>>> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > >>>> index 7c67ac6f08df..d1847f29f59b 100644 > >>>> --- a/arch/arm64/kernel/mte.c > >>>> +++ b/arch/arm64/kernel/mte.c > >>>> @@ -23,6 +23,8 @@ > >>>> #include > >>>> #include > >>>> > >>>> +u64 gcr_kernel_excl __ro_after_init; > >>>> + > >>>> static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > >>>> { > >>>> pte_t old_pte = READ_ONCE(*ptep); > >>>> @@ -120,6 +122,13 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag) > >>>> return ptr; > >>>> } > >>>> > >>>> +void mte_init_tags(u64 max_tag) > >>>> +{ > >>>> + u64 incl = GENMASK(max_tag & MTE_TAG_MAX, 0); > >>> > >>> Nitpick: it's not obvious that MTE_TAG_MAX is a mask, so better write > >>> this as GENMASK(min(max_tag, MTE_TAG_MAX), 0). > >> > >> The two things do not seem equivalent because the format of the tags in KASAN is > >> 0xFF and in MTE is 0xF, hence if extract the minimum whatever is the tag passed > >> by KASAN it will always be MTE_TAG_MAX. > >> > >> To make it cleaner I propose: GENMASK(FIELD_GET(MTE_TAG_MAX, max_tag), 0); > > > > I don't think that's any clearer since FIELD_GET still assumes that > > MTE_TAG_MAX is a mask. I think it's better to add a comment on why this > > is needed, as you explained above that the KASAN tags go to 0xff. > > > > If you want to get rid of MTE_TAG_MAX altogether, just do a > > > > max_tag &= (1 << MAX_TAG_SIZE) - 1; > > > > before setting incl (a comment is still useful). > > > > Agree, but still think we should use FIELD_GET here since it is common language > in the kernel. > > How about we get rid of MTE_TAG_MAX and we do something like: > > GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT, max_tag), 0); It works for me and you can drop the MTE_TAG_MAX definition (I think it's only used here). -- Catalin