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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 7EC45ECDE32 for ; Wed, 17 Oct 2018 11:15:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 29C0E2150D for ; Wed, 17 Oct 2018 11:15:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 29C0E2150D 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727061AbeJQTLA (ORCPT ); Wed, 17 Oct 2018 15:11:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:45294 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726922AbeJQTLA (ORCPT ); Wed, 17 Oct 2018 15:11:00 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6E62CAD21; Wed, 17 Oct 2018 11:15:45 +0000 (UTC) Date: Wed, 17 Oct 2018 13:15:44 +0200 From: Michal Hocko To: Pavel Machek Cc: vbabka@suse.cz, hpa@zytor.com, torvalds@linux-foundation.org, ak@linux.intel.com, dave.hansen@intel.com, kernel list , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de Subject: Re: l1tf: Kernel suggests I throw away third of my memory. I'd rather not Message-ID: <20181017111544.GO18839@dhcp22.suse.cz> References: <20181017105610.GA4260@amd> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181017105610.GA4260@amd> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 17-10-18 12:56:10, Pavel Machek wrote: > Hi! > > 6a012288 suggests I throw away 1GB on RAM. On 3GB system.. that is not > going to be pleasant. > > l1tf.html says: > > # The Linux kernel contains a mitigation for this attack vector, PTE > # inversion, which is permanently enabled and has no performance > # impact. > > I don't believe it has "no" performance impact, but I guess it is lost > in the noise. Please prove otherwise. I would be more than surprised if inverting pfn part of the pte is noticeable. But I can be wrong of course. > # The kernel ensures that the address bits of PTEs, which are > # not marked present, never point to cacheable physical memory space. > > # A system with an up to date kernel is protected against attacks from > # malicious user space applications. > > These are not true. > > cat /sys/devices/system/cpu/vulnerabilities/l1tf > Vulnerable > uname -a > Linux amd 4.19.0-rc8-next-20181017autobisect1539371050 #189 SMP Wed > Oct 17 12:04:23 CEST 2018 i686 GNU/Linux This is a result of you having memory above MAX_PFN/2 right? > Now question is... can we do better? Kernel stores information about > swapped-out pages there, right? That sounds like a cool hack, but > maybe it is time to get rid of that hack? Patches are welcome. > As a workaround, can I simply do swapoff -a to be safe for now? Well, that depends. Do you care about PROT_NONE attacks as well? If not then no-swap would help you. But even then no-swap is rather theoretical attack on a physical host unless you allow an arbitrary swapout to a malicious user (e.g. allow a user controlled memcg hard limit that would cause excessive local swapouts). -- Michal Hocko SUSE Labs