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=-13.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 602CEC433E1 for ; Thu, 23 Jul 2020 19:33:56 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2CBDE20737 for ; Thu, 23 Jul 2020 19:33:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CBDE20737 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 9951A6B0007; Thu, 23 Jul 2020 15:33:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9462F6B000C; Thu, 23 Jul 2020 15:33:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 834A56B000D; Thu, 23 Jul 2020 15:33:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0052.hostedemail.com [216.40.44.52]) by kanga.kvack.org (Postfix) with ESMTP id 6E7FE6B0007 for ; Thu, 23 Jul 2020 15:33:55 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 18132181AEF3F for ; Thu, 23 Jul 2020 19:33:55 +0000 (UTC) X-FDA: 77070340830.04.eyes95_5112f2f26f41 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id EA0E6800CE19 for ; Thu, 23 Jul 2020 19:33:54 +0000 (UTC) X-HE-Tag: eyes95_5112f2f26f41 X-Filterd-Recvd-Size: 4404 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Thu, 23 Jul 2020 19:33:54 +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 73CF2D6E; Thu, 23 Jul 2020 12:33:53 -0700 (PDT) Received: from [192.168.178.35] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E7E3F3F66E; Thu, 23 Jul 2020 12:33:51 -0700 (PDT) Subject: Re: [PATCH v7 18/29] arm64: mte: Allow user control of the tag check mode via prctl() To: Dave Martin 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 References: <20200715170844.30064-1-catalin.marinas@arm.com> <20200715170844.30064-19-catalin.marinas@arm.com> <20200720170050.GJ30452@arm.com> From: Kevin Brodsky Message-ID: Date: Thu, 23 Jul 2020 20:33:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 MIME-Version: 1.0 In-Reply-To: <20200720170050.GJ30452@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-GB X-Rspamd-Queue-Id: EA0E6800CE19 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 20/07/2020 18:00, Dave Martin wrote: > 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? Isn't it as simple as checking if PF_KTHREAD is set in tsk->flags? At least this is what ssbs_thread_switch() does. Kevin > 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