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,INCLUDES_PATCH,MAILING_LIST_MULTI,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 7C88FC4363A for ; Mon, 26 Oct 2020 13:15:47 +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 26BF42080A for ; Mon, 26 Oct 2020 13:15:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="HhO0vFUc"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="zoRIHOuT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 26BF42080A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=02KInI3Ei4K2SFIULE8B/oz+xJAq742Hmw/AA0PMlPw=; b=HhO0vFUcRGmCNHPGq6w7IZ+Tj KpwFOBnpInKqdFDnR7sLr4jEtSvF4+LQ70PQInGxhDmMS7ttWB9QeWP9Pq48MaaeSokMQ/BZMtwof m1bPzi49O3wXhRcJOzS2y0IY/KGnz8HRJspClzBLvPSLhT+sf1elm/INL/D0Oi9LQCdW0tOHrRciU vuUc1qdpsy3wTU4GQKNyH7J1TlE4YExWLeWwoyc25Tpz20iRicWDHew57w4QgcBQRm884+ewNFmBD DjkotWxaZ91+6k+acyVp/tjJzs18BW7Uis7aZ9u1b/DYOBZ9rAoKaMT1+Ek4p1PjVYVLG6gI/qBcm Qbx77MaqA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kX2KQ-00036e-EM; Mon, 26 Oct 2020 13:14:26 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kX2KL-00035G-7y for linux-arm-kernel@lists.infradead.org; Mon, 26 Oct 2020 13:14:22 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8B0022080A; Mon, 26 Oct 2020 13:14:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603718059; bh=HfnrTImzbJN/Q1Q9IXoHw59lr9uvygqcjNhG0HGu1WY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=zoRIHOuTSr24qhAeMuCJmP9v+/JyBjgHIgaQ12xy8Qe2QCjUjiTttHD6kdzP84/sT jm+hV+hfpUY7/1lCsyFy5iL8QvhtBMj0w1I8PoL82HtTiFy/l1jtjUjUKApYa2K5JB Ufn70J3b3JgUIcFgeqRJOJc3hLHz8yjc0iIcWtr4= Date: Mon, 26 Oct 2020 13:14:15 +0000 From: Will Deacon To: Catalin Marinas Subject: Re: [PATCH] arm64: mte: Document that user PSTATE.TCO is ignored by kernel uaccess Message-ID: <20201026131414.GA24349@willie-the-truck> References: <20201026121656.26096-1-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201026121656.26096-1-catalin.marinas@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201026_091421_414336_F04BA495 X-CRM114-Status: GOOD ( 21.58 ) 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: Branislav Rankov , Szabolcs Nagy , andreyknvl@google.com, Vincenzo Frascino , pcc@google.com, 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, Oct 26, 2020 at 12:16:56PM +0000, 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 > --- > 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. nit, but the wording feels a bit odd to me here. How about: Kernel accesses to user addresses are always performed with an effective PSTATE.TCO value of zero, regardless of the user configuration. ? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel