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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 84C28C43331 for ; Fri, 3 Apr 2020 17:21:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2F472206F5 for ; Fri, 3 Apr 2020 17:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404367AbgDCRVa (ORCPT ); Fri, 3 Apr 2020 13:21:30 -0400 Received: from mga05.intel.com ([192.55.52.43]:43136 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728066AbgDCRV3 (ORCPT ); Fri, 3 Apr 2020 13:21:29 -0400 IronPort-SDR: fjEhpCPcyAdxUQARVqP1s0WxMK+ndckAzcxa5q5ytgqf4m1qVX+UWht5ATTuz1EBZlZoqaF0tN wZKABqg8jeAA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2020 10:21:29 -0700 IronPort-SDR: EC4hJqgWCgeSPdQln89njVGtlG/mPy3BJRJGwOAC97Oaga7gQcH6kLrT2irhhGcfkUHziSiEGv U8d7vxVtZ5Sw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,340,1580803200"; d="scan'208";a="243509627" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga008.jf.intel.com with ESMTP; 03 Apr 2020 10:21:29 -0700 Date: Fri, 3 Apr 2020 10:21:29 -0700 From: Sean Christopherson To: Nadav Amit Cc: Peter Zijlstra , Jessica Yu , Rasmus Villemoes , Thomas Gleixner , LKML , x86 , "Kenneth R. Crudup" , Paolo Bonzini , Fenghua Yu , Xiaoyao Li , Thomas Hellstrom , Tony Luck , Steven Rostedt , Greg Kroah-Hartman , "jannh@google.com" , "keescook@chromium.org" Subject: Re: [patch 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect Message-ID: <20200403172129.GE2701@linux.intel.com> References: <20200402123258.895628824@linutronix.de> <20200402124205.242674296@linutronix.de> <20200403143459.GA30424@linux-8ccs> <20200403152158.GR20730@hirez.programming.kicks-ass.net> <20200403160156.GA2701@linux.intel.com> <20200403161205.GT20730@hirez.programming.kicks-ass.net> <20200403162555.GB2701@linux.intel.com> <20200403164058.GX20730@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 03, 2020 at 04:48:35PM +0000, Nadav Amit wrote: > > On Apr 3, 2020, at 9:40 AM, Peter Zijlstra wrote: > > > > On Fri, Apr 03, 2020 at 09:25:55AM -0700, Sean Christopherson wrote: > >> On Fri, Apr 03, 2020 at 06:12:05PM +0200, Peter Zijlstra wrote: > >>> On Fri, Apr 03, 2020 at 09:01:56AM -0700, Sean Christopherson wrote: > >>>> On Fri, Apr 03, 2020 at 05:21:58PM +0200, Peter Zijlstra wrote: > >>>>> On Fri, Apr 03, 2020 at 04:35:00PM +0200, Jessica Yu wrote: > >>> > >>>>>> I wonder if it would make sense then to limit the text scans to just > >>>>>> out-of-tree modules (i.e., missing the intree modinfo flag)? > >>>>> > >>>>> It would; didn't know there was one. > >>>> > >>>> Rather than scanning modules at all, what about hooking native_write_cr4() > >>>> to kill SLD if CR4.VMXE is toggled on and the caller didn't increment a > >>>> "sld safe" counter? > >>> > >>> And then you're hoping that the module uses that and not: > >>> > >>> asm volatile ("mov %0, cr4" :: "r" (val)); > >>> > >>> I think I feel safer with the scanning to be fair. Also with the intree > >>> hint on, we can extend the scanning for out-of-tree modules for more > >>> dodgy crap we really don't want modules to do, like for example the > >>> above. > >> > >> Ya, that's the big uknown. But wouldn't they'd already be broken in the > >> sense that they'd corrupt the CR4 shadow? E.g. setting VMXE without > >> updating cpu_tlbstate.cr4 would result in future in-kernel writes to CR4 > >> attempting to clear CR4.VMXE post-VMXON, which would #GP. > > > > Sadly the CR4 shadow is exported, so they can actually fix that up :/ > > I do not think that Sean’s idea would work for VMware. Well phooey.