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,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 E14BBC433E0 for ; Mon, 20 Jul 2020 17:02:17 +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 AAF37206E9 for ; Mon, 20 Jul 2020 17:02:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="dOKw+JE0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AAF37206E9 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-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=MhK1iPdMCebs319zgtXJKyYv36afnmUIhBqxtLIoo6Q=; b=dOKw+JE0Kdlrqefhvzby2pfej eV/nemo+MTXiCQWc+Arum6DrhQQpFqGoqFUTh5RuU+kD+EpYR1sm+STR62q2Vm+4fqJsXcT0zHwyx k8vVeAjVIhVCH97Re4LH4dORQcOn0KhqjdJ5PlzOSNOyZDkc67CFsLK4vTItrDX9rPDYM0yfT3JZV mhUY5wJ2sPXDRZI86opzHGQ+oLIXhVUIJ+mcjRJhuyjRK7xDGxIB5iLBmL+zGA6S511HsrroyHviu enntOTrMfdNOCbtHud5Lwlj6UEnq8auB8lz68ipb1iAo48zfmtIQogYcpwKDrmCHCUs4rMMLaSk8B BfALdqMdQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jxZ9t-0000tf-DY; Mon, 20 Jul 2020 17:00:57 +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 1jxZ9r-0000t4-AE for linux-arm-kernel@lists.infradead.org; Mon, 20 Jul 2020 17:00:56 +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 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 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-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200720_130055_429805_FF9DE4AB X-CRM114-Status: GOOD ( 25.45 ) 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel