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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 E5AFFC43331 for ; Fri, 3 Apr 2020 16:25:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C4AE72073B for ; Fri, 3 Apr 2020 16:25:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404513AbgDCQZ4 (ORCPT ); Fri, 3 Apr 2020 12:25:56 -0400 Received: from mga18.intel.com ([134.134.136.126]:5286 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404417AbgDCQZ4 (ORCPT ); Fri, 3 Apr 2020 12:25:56 -0400 IronPort-SDR: Zn9SOuU4lVx2GPQNj6rAOdH0QQIff4D2Sx9RX5brSd4odxu8/uRs3ZlUPtKNVTmBB6LN1Uo6rI pDtTN0onWzfw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2020 09:25:55 -0700 IronPort-SDR: NJKD4tXFCPQdgi8RjmGj0ABHDBmsbihKVMaREI2i4yehHhZzEdi7VL22ptJtgHf5flw8GOEECA xdn/HKcAi9NQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,340,1580803200"; d="scan'208";a="396786260" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga004.jf.intel.com with ESMTP; 03 Apr 2020 09:25:55 -0700 Date: Fri, 3 Apr 2020 09:25:55 -0700 From: Sean Christopherson To: Peter Zijlstra Cc: Jessica Yu , Rasmus Villemoes , Thomas Gleixner , LKML , x86@kernel.org, "Kenneth R. Crudup" , Paolo Bonzini , Fenghua Yu , Xiaoyao Li , Nadav Amit , 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: <20200403162555.GB2701@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200403161205.GT20730@hirez.programming.kicks-ass.net> 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 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.