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=-5.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 05C6DC3A5A9 for ; Mon, 4 May 2020 17:03:31 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 C192820721 for ; Mon, 4 May 2020 17:03:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ugHuaGSO"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="mxP6h5LV" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C192820721 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+infradead-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=bombadil.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=uRjCEQTOrGMtKkeQnbuzHTvm7KWVCJDwyxnbEvxxHVk=; b=ugHuaGSOTHWjub ecO5HYG6mPk4bLa5PE0uTdnkCtMIoiI8XyhSAaT0sNHkeNLHuhyTJ3fDWuxdde/0O+dHvd/qEShfk SMBcANlc6l5WOVzzdttAGiK0HGjzEMZ43xCzMyouUjf0uAJGI8wlBlce12qeAqVirux3hdgbQtAe0 qQHTCQcNY41O1oRsyDH3QJ9Zq0qPNgDKOxO5+FRnR/rvPSPC8mXG9/cyjvA6wNAxu4cWXAssxqlKl laQWHftWjfM2ZpuQSt85QvrXqzFLC7+JYW39QSZKkomF/ky5NborjfxYrWDBB0n2FrT74K3M4hVUG m2zVRKH+Puk6bRugGJLw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVeV8-00076c-75; Mon, 04 May 2020 17:03:30 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jVeV4-00075l-MP for linux-arm-kernel@lists.infradead.org; Mon, 04 May 2020 17:03:28 +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 A46D8206D7; Mon, 4 May 2020 17:03:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588611806; bh=9tTj22KeXXNy+Pxbwwax2L1FDq1F5u2WKlSPld/o7ug=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mxP6h5LVA5K0vlpO9F/T9qh1mMYOmFIcBdnnPlf9OSLhUyYihlx1c6R5/EiJqSjce s37jTncHdY+7uJQEoA9A+WdZlCbYF3sj6YDHhNNHFOu2jRZc4bYPf/DnnTbp71TX+B Af8TheWZp+1X27mXtE9UPQn0yHEH65ELvxPAfkM0= Date: Mon, 4 May 2020 18:03:21 +0100 From: Will Deacon To: Peter Collingbourne Subject: Re: [PATCH v3] arm64: Expose original FAR_EL1 value in sigcontext Message-ID: <20200504170320.GC1833@willie-the-truck> References: <20200325174001.234803-1-pcc@google.com> <20200327191915.257116-1-pcc@google.com> <20200429210826.GA8604@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: 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-20200504_100326_751962_1CCFF946 X-CRM114-Status: GOOD ( 17.21 ) 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: Catalin Marinas , Kevin Brodsky , Kostya Serebryany , Evgenii Stepanov , Andrey Konovalov , Vincenzo Frascino , Linux ARM , Richard Henderson Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Peter, On Wed, Apr 29, 2020 at 02:42:01PM -0700, Peter Collingbourne wrote: > On Wed, Apr 29, 2020 at 2:08 PM Will Deacon wrote: > > On Fri, Mar 27, 2020 at 12:19:15PM -0700, Peter Collingbourne wrote: > > > The kernel currently clears the tag bits (i.e. bits 56-63) in the fault > > > address exposed via siginfo.si_addr and sigcontext.fault_address. However, > > > the tag bits may be needed by tools in order to accurately diagnose > > > memory errors, such as HWASan [1] or future tools based on the Memory > > > Tagging Extension (MTE). > > > > > > We should not stop clearing these bits in the existing fault address > > > fields, because there may be existing userspace applications that are > > > expecting the tag bits to be cleared. Instead, create a far_context in > > > sigcontext (similar to the existing esr_context), and store the original > > > value of FAR_EL1 (including the tag bits) there. > > > > > > [1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html > > > > > > Signed-off-by: Peter Collingbourne > > > --- > > > v3: > > > - add documentation to tagged-pointers.rst > > > - update comments in sigcontext.h > > > > Hmm, although the code looks fine, why don't we just expose the tag in the > > new field, rather than duplicate the address information? I'm nervous about > > exposing privileged registers directly to userspace. > > I have no strong opinion on whether this should just contain the tag or not. A few of us chatted about this today. Please could you spin a v4 where only the top byte is exposed in the new sigcontext record as a __u8? You'll need to think of a better name than "FAR"; perhaps something like 'si_addr_top_byte', 'si_addr_63_56' or whatever you fancy. Naming is hard. For MTE we can add a separate record later on, so as not to overload this (e.g. si_addr_mte_tag). Ta, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel