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=-13.4 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=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 7C5C7C2D0A3 for ; Mon, 26 Oct 2020 12:24:54 +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 2EA6920882 for ; Mon, 26 Oct 2020 12:24:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ObcWnYyv" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2EA6920882 Authentication-Results: mail.kernel.org; dmarc=fail (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: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=FO4N+e+YMbHbVZyOjk2mw2bLTQAohIZ83DHsH7fsFE0=; b=ObcWnYyvlnl4Z6fJdQpl9t+UB PR+xk46Rgf++lqERWXy8z4XJ5xKw0VZ2YDkh6fpQnZpjbrfE/glZ2yD9bCIdWcmcabr4c8ZA/DdfJ EtlrlcYXvL6XRIv6y5VVmDFL4CDHtvduQ5iMkPrVVzbW2uBrTM3LzUi9mqDqxf+UZV6oGGdbOMWFs E/U+O5KjbzlJ3ixWK6YYT6RcYtf2ZP+QN3e1i1Zfwsy6/IVETOWFfxXupWwvETHhtYKIR6K9MD8a2 /LmsL0w38Wvl6HjIAe6pueGHxKXz7umQuZwMY9hsm3Z3QvEEGfB60AuAiXBjIfFqZ8/u6ELKeeVlB gIqi8pOwQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kX1X5-00067X-Mw; Mon, 26 Oct 2020 12:23:27 +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 1kX1X3-000679-6P for linux-arm-kernel@lists.infradead.org; Mon, 26 Oct 2020 12:23:26 +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 92F0A1477; Mon, 26 Oct 2020 05:23:23 -0700 (PDT) Received: from [10.37.12.42] (unknown [10.37.12.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 603C33F719; Mon, 26 Oct 2020 05:23:22 -0700 (PDT) Subject: Re: [PATCH] arm64: mte: Document that user PSTATE.TCO is ignored by kernel uaccess To: Catalin Marinas , linux-arm-kernel@lists.infradead.org, Will Deacon References: <20201026121656.26096-1-catalin.marinas@arm.com> From: Vincenzo Frascino Message-ID: <2ddd7756-364f-a4d8-5ef1-c824290751b8@arm.com> Date: Mon, 26 Oct 2020 12:26:16 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201026121656.26096-1-catalin.marinas@arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201026_082325_315957_AA34A428 X-CRM114-Status: GOOD ( 24.05 ) 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: Szabolcs Nagy , andreyknvl@google.com, Branislav Rankov , pcc@google.com 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 10/26/20 12:16 PM, Catalin Marinas wrote: > On exception entry, the kernel explicitly resets the PSTATE.TCO (tag > check override) so that any kernel memory accesses will be checked (the > bit is restored on exception return). This has the side-effect that the > uaccess routines will not honour the PSTATE.TCO that may have been set > by the user prior to a syscall. > > There is no issue in practice since PSTATE.TCO is expected to be used > only for brief periods in specific routines (e.g. garbage collection). > To control the tag checking mode of the uaccess routines, the user will > have to invoke a corresponding prctl() call. > > Document the kernel behaviour w.r.t. PSTATE.TCO accordingly. > > Signed-off-by: Catalin Marinas > Fixes: df9d7a22dd21 ("arm64: mte: Add Memory Tagging Extension documentation") > Cc: Will Deacon > Cc: Szabolcs Nagy It is a good thing that we are documenting this explicitly since it might be confusing to the user why the kernel behaves in a certain way. Reviewed-by: Vincenzo Frascino > --- > Documentation/arm64/memory-tagging-extension.rst | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/Documentation/arm64/memory-tagging-extension.rst b/Documentation/arm64/memory-tagging-extension.rst > index 034d37c605e8..648f8e8d480b 100644 > --- a/Documentation/arm64/memory-tagging-extension.rst > +++ b/Documentation/arm64/memory-tagging-extension.rst > @@ -102,7 +102,9 @@ applications. > system call) are not checked if the user thread tag checking mode is > ``PR_MTE_TCF_NONE`` or ``PR_MTE_TCF_ASYNC``. If the tag checking mode is > ``PR_MTE_TCF_SYNC``, the kernel makes a best effort to check its user > -address accesses, however it cannot always guarantee it. > +address accesses, however it cannot always guarantee it. The user > +``PSTATE.TCO`` bit is ignored by the kernel accesses to user addresses, > +its value assumed 0. > > Excluding Tags in the ``IRG``, ``ADDG`` and ``SUBG`` instructions > ----------------------------------------------------------------- > -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel