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,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 B5B6FC433E5 for ; Thu, 23 Jul 2020 19:35:44 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7D0812065F for ; Thu, 23 Jul 2020 19:35:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="QSOoc/CO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7D0812065F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XndLN9/3YgrMCIrxX6duGOdDLtxI4ZvKfAeRSrvvWfE=; b=QSOoc/COMrL8Rmq35f3lNREmO BB/SImk0nA7TCuL6VoVzf4fdisMaFvJUV/YoCXdYeqIh+GwhroVnsE/Y00TiyGf6qiBM+Q/IIJTRC 7AGvc/G9F4qwkDwmFP7m3+JHI8PzFT0HbjqrG6H1YNlBchd4/C4VCux2nKyk8w+v5V1eqHdM3Oqjn Gcq8v5ml9SNRKFXMuoEUUfq/TkZmKc8yTBYtR/nBowIk8YjDl/PUvu0Kxd/5gK55ebYjNqtrC1+2x VeQRtC3QaYsnbV+9kMWF1a+RHXrpMwr2v2aUPSqu0DY/kcNOeDHngraTiZ/uO61ms2R3o9MZj+YMN XZ172YGTg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jygyj-00077D-RW; Thu, 23 Jul 2020 19:34:05 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jygyg-00076a-UL for linux-arm-kernel@lists.infradead.org; Thu, 23 Jul 2020 19:34:03 +0000 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 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-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200723_153403_070370_1E97FE38 X-CRM114-Status: GOOD ( 22.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Will Deacon , Szabolcs Nagy , Catalin Marinas , linux-mm@kvack.org, Andrey Konovalov , Andrew Morton , Vincenzo Frascino , Peter Collingbourne , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel