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=-11.3 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,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 60D37C4363A for ; Mon, 26 Oct 2020 14:19:26 +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 13ECD21655 for ; Mon, 26 Oct 2020 14:19:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="FytsP6R8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 13ECD21655 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: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=4b1zDH6Y4gO7TX0WlrllLKtYOGN4afLj7uBMcAldvl8=; b=FytsP6R8VgB1oMxWZ57MIdFwZ h5XLfsqyodJ/UCA1ZUInO9pxrthzAShJsDw/isbw7mOK3/2mcUKS6e5I6Zz8Xnsckg3LZmhjuh8lC NZb3QAkMDI9lWd/u++wp1sXgm94bBHn4TMcX43HtzeznHrSCIoZdEWvTIx7osrmolerxIJW8GvnEw C/pPovspkkWePMNjSocijcQX9Lh9xvKcy3xgOBWn7ec64NbQQawFRuSt0n1n8GoEmO7nsk7qRaG/x KQcvKYVWP0/HNsbrdeoKMNFndoxo4UNsS/26yyGZ1jabhoQ+6m4Br5YUxpXkYOwFYXbSU7utx8gO6 U1DGiGLSw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kX3K3-0005fr-Ik; Mon, 26 Oct 2020 14:18:07 +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 1kX3K1-0005fR-AJ for linux-arm-kernel@lists.infradead.org; Mon, 26 Oct 2020 14:18:06 +0000 Received: from gaia (unknown [95.145.162.19]) (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 7BA6421655; Mon, 26 Oct 2020 14:18:02 +0000 (UTC) Date: Mon, 26 Oct 2020 14:18:00 +0000 From: Catalin Marinas To: Will Deacon Subject: Re: [PATCH] arm64: mte: Document that user PSTATE.TCO is ignored by kernel uaccess Message-ID: <20201026141759.GC3117@gaia> References: <20201026121656.26096-1-catalin.marinas@arm.com> <20201026131414.GA24349@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201026131414.GA24349@willie-the-truck> 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_101805_427484_9597DA88 X-CRM114-Status: GOOD ( 24.62 ) 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 01:14:15PM +0000, Will Deacon wrote: > 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. That's better. Thanks. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel