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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1CA36C46467 for ; Wed, 11 Jan 2023 00:13:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235543AbjAKAN3 (ORCPT ); Tue, 10 Jan 2023 19:13:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37460 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231265AbjAKAN0 (ORCPT ); Tue, 10 Jan 2023 19:13:26 -0500 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C685D5B157 for ; Tue, 10 Jan 2023 16:13:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1673396005; x=1704932005; h=message-id:date:mime-version:subject:to:references:from: in-reply-to:content-transfer-encoding; bh=rhBvEIso996KWiUYNT3v6A5OEIDRuz0ouJ0cSkwqISA=; b=SeaUjaXlKk+Me4ag+2tnt/OHPJ/oAIIVhh9JcMcMPOtlZxKzx9Fw/asQ aPn8UA1Vjt4Ylnja0oLYi+EAZUKI0kVeUhKmAAKO/QnC46FRkpTUh+yB/ nW1SneYAf3yLOlw7YGmgBPwWmt1iVgj5ERMv1b4Qk1Eh5SbmMBjW9FEzf Nt7C64df4RZKXXhOuj32/6i4vnQn6knDJjf77BalTcub0//UB/BWK3OgO BLp+pKaynZbjewB7mdgrMfywo8OGg1MvG+pGUHrhtocinZvRjNGIKx0hq krycIfJFwszpoX5C6Z5T1FcU2uEleppx3EjTt9P3bu+8/ODsUV3MnV6da Q==; X-IronPort-AV: E=McAfee;i="6500,9779,10586"; a="311101652" X-IronPort-AV: E=Sophos;i="5.96,315,1665471600"; d="scan'208";a="311101652" Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jan 2023 16:13:25 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10586"; a="725713580" X-IronPort-AV: E=Sophos;i="5.96,315,1665471600"; d="scan'208";a="725713580" Received: from svenka7-mobl1.amr.corp.intel.com (HELO [10.209.63.27]) ([10.209.63.27]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jan 2023 16:13:20 -0800 Message-ID: Date: Tue, 10 Jan 2023 16:13:18 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH 1/7] x86/cpu: Enumerate LASS CPUID and CR4 bits Content-Language: en-US To: Sohil Mehta , Yian Chen , linux-kernel@vger.kernel.org, x86@kernel.org, Andy Lutomirski , Dave Hansen , Ravi Shankar , Tony Luck , Paul Lai References: <20230110055204.3227669-1-yian.chen@intel.com> <20230110055204.3227669-2-yian.chen@intel.com> <9d935618-8f84-2d6e-4f4c-9d38eec2ba67@intel.com> From: Dave Hansen In-Reply-To: <9d935618-8f84-2d6e-4f4c-9d38eec2ba67@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/10/23 12:14, Sohil Mehta wrote: > On 1/9/2023 9:51 PM, Yian Chen wrote: >> LASS (Linear Address Space Separation) is a CPU feature to >> prevent speculative address access in user/kernel mode. > > Would it be better to say? > > LASS (Linear Address Space Separation) is a security feature that > intends to prevent unintentional speculative address access across > user/kernel mode. It's more than that, though. The spec actually says this pretty nicely: > Linear-address space separation (LASS) is an independent mechanism > that enforces the same mode-based protections as paging but without > traversing the paging structures. Because the protections enforced by > LASS are applied before paging, “probes” by malicious software will > provide no paging-based timing information So, it's not _just_ that it can prevent some speculative accesses. It completely short-circuits paging itself and *ALL* of the baggage that goes along with paging. The TLB, mid-level caches, the page walker itself, the data cache impact... all of it. Gone. *THAT* is the important part here, IMNHO.