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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 AF389C433E0 for ; Mon, 20 Jul 2020 17:11:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 607FF2176B for ; Mon, 20 Jul 2020 17:11:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 607FF2176B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C267D6B0002; Mon, 20 Jul 2020 13:11:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id BD5CB6B0005; Mon, 20 Jul 2020 13:11:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A9CD86B0006; Mon, 20 Jul 2020 13:11:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0219.hostedemail.com [216.40.44.219]) by kanga.kvack.org (Postfix) with ESMTP id 901EF6B0002 for ; Mon, 20 Jul 2020 13:11:02 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 2FD325CA56F7 for ; Mon, 20 Jul 2020 17:11:02 +0000 (UTC) X-FDA: 77059094364.16.oil38_3a0303426f26 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id 4877C100C0586 for ; Mon, 20 Jul 2020 17:00:55 +0000 (UTC) X-HE-Tag: oil38_3a0303426f26 X-Filterd-Recvd-Size: 4068 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Mon, 20 Jul 2020 17:00:54 +0000 (UTC) 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 C62AE106F; Mon, 20 Jul 2020 10:00:53 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5BCD03F66E; Mon, 20 Jul 2020 10:00:52 -0700 (PDT) Date: Mon, 20 Jul 2020 18:00:50 +0100 From: Dave Martin To: Kevin Brodsky Cc: Catalin Marinas , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, Szabolcs Nagy , Andrey Konovalov , Peter Collingbourne , linux-mm@kvack.org, Andrew Morton , Vincenzo Frascino , Will Deacon Subject: Re: [PATCH v7 18/29] arm64: mte: Allow user control of the tag check mode via prctl() Message-ID: <20200720170050.GJ30452@arm.com> References: <20200715170844.30064-1-catalin.marinas@arm.com> <20200715170844.30064-19-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-Rspamd-Queue-Id: 4877C100C0586 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jul 20, 2020 at 04:30:35PM +0100, Kevin Brodsky wrote: > On 15/07/2020 18:08, Catalin Marinas wrote: > >By default, even if PROT_MTE is set on a memory range, there is no tag > >check fault reporting (SIGSEGV). Introduce a set of option to the > >exiting prctl(PR_SET_TAGGED_ADDR_CTRL) to allow user control of the tag > >check fault mode: > > > > PR_MTE_TCF_NONE - no reporting (default) > > PR_MTE_TCF_SYNC - synchronous tag check fault reporting > > PR_MTE_TCF_ASYNC - asynchronous tag check fault reporting > > > >These options translate into the corresponding SCTLR_EL1.TCF0 bitfield, > >context-switched by the kernel. Note that uaccess done by the kernel is > >not checked and cannot be configured by the user. > > > >Signed-off-by: Catalin Marinas > >Cc: Will Deacon > >--- > > > >Notes: > > v3: > > - Use SCTLR_EL1_TCF0_NONE instead of 0 for consistency. > > - Move mte_thread_switch() in this patch from an earlier one. In > > addition, it is called after the dsb() in __switch_to() so that any > > asynchronous tag check faults have been registered in the TFSR_EL1 > > registers (to be added with the in-kernel MTE support. > > v2: > > - Handle SCTLR_EL1_TCF0_NONE explicitly for consistency with PR_MTE_TCF_NONE. > > - Fix SCTLR_EL1 register setting in flush_mte_state() (thanks to Peter > > Collingbourne). > > - Added ISB to update_sctlr_el1_tcf0() since, with the latest > > architecture update/fix, the TCF0 field is used by the uaccess > > routines. [...] > >diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c [...] > >+void mte_thread_switch(struct task_struct *next) > >+{ > >+ if (!system_supports_mte()) > >+ return; > >+ > >+ /* avoid expensive SCTLR_EL1 accesses if no change */ > >+ if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0) > > I think this could be improved by checking whether `next` is a kernel > thread, in which case thread.sctlr_tcf0 is 0 but there is no point in > setting SCTLR_EL1.TCF0, since there should not be any access via TTBR0. Out of interest, do we have a nice way of testing for a kernel thread now? I remember fpsimd_thread_switch() used to check for task->mm, but we seem to have got rid of that at some point. set_mm() can defeat this, and anyway the heavy lifting for FPSIMD is now deferred until returning to userspace. Cheers ---Dave