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=-10.3 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 094E2C433B4 for ; Tue, 4 May 2021 15:29:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDDF06008E for ; Tue, 4 May 2021 15:29:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230396AbhEDPam (ORCPT ); Tue, 4 May 2021 11:30:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:58354 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230212AbhEDPal (ORCPT ); Tue, 4 May 2021 11:30:41 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1BDA060FDC; Tue, 4 May 2021 15:29:42 +0000 (UTC) Date: Tue, 4 May 2021 16:29:40 +0100 From: Catalin Marinas To: Steven Price Cc: Marc Zyngier , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Haibo Xu , Andrew Jones Subject: Re: [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged Message-ID: <20210504152938.GC8078@arm.com> References: <20210416154309.22129-1-steven.price@arm.com> <20210416154309.22129-2-steven.price@arm.com> <20210427174357.GA17872@arm.com> <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 29, 2021 at 05:06:05PM +0100, Steven Price wrote: > On 27/04/2021 18:43, Catalin Marinas wrote: > > On Fri, Apr 16, 2021 at 04:43:04PM +0100, Steven Price wrote: > > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > > > index e17b96d0e4b5..cf4b52a33b3c 100644 > > > --- a/arch/arm64/include/asm/pgtable.h > > > +++ b/arch/arm64/include/asm/pgtable.h > > > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > > > __sync_icache_dcache(pte); > > > if (system_supports_mte() && > > > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte)) > > > + pte_present(pte) && (pte_val(pte) & PTE_USER) && !pte_special(pte)) > > > > I would add a pte_user() macro here or, if we restore the tags only when > > the page is readable, use pte_access_permitted(pte, false). Also add a > > comment why we do this. > > pte_access_permitted() looks like it describes what we want (user space can > access the memory). I'll add the following comment: > > /* > * If the PTE would provide user space will access to the tags I think drop "will". > * associated with it then ensure that the MTE tags are synchronised. > * Exec-only mappings don't expose tags (instruction fetches don't > * check tags). > */ Sounds fine. > > There's also the pte_user_exec() case which may not have the PTE_USER > > set (exec-only permission) but I don't think it matters. We don't do tag > > checking on instruction fetches, so if the user adds a PROT_READ to it, > > it would go through set_pte_at() again. I'm not sure KVM does anything > > special with exec-only mappings at stage 2, I suspect they won't be > > accessible by the guest (but needs checking). > > It comes down to the behaviour of get_user_pages(). AFAICT that will fail if > the memory is exec-only, so no stage 2 mapping will be created. Which of > course means the guest can't do anything with that memory. That certainly > seems like the only sane behaviour even without MTE. That's my understanding as well. The get_user_pages_fast() path uses pte_access_permitted() and should return false. The slower get_user_pages() relies on checking the vma flags and it checks for VM_READ. -- Catalin