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=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 80BA2C433DF for ; Tue, 23 Jun 2020 15:39:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 629BE20774 for ; Tue, 23 Jun 2020 15:39:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733056AbgFWPjd (ORCPT ); Tue, 23 Jun 2020 11:39:33 -0400 Received: from esa1.hc3370-68.iphmx.com ([216.71.145.142]:56281 "EHLO esa1.hc3370-68.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732978AbgFWPjc (ORCPT ); Tue, 23 Jun 2020 11:39:32 -0400 Authentication-Results: esa1.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none IronPort-SDR: eiqxVBWKC88b1iIh5nTj/f7V8Jh2ethNUebZFkujWdRGxn9kUdey47KybRdBPzpPU3UaTmRUbu hhEzIKGB0mKgn/ZmC+NiJ8ZJHLfOksnJ/vSslBnIPYj9seYdLRSUz7dZQO5BZc0yl6bA4IjueI bn/dF7MfxrIDT5AJWZamzmm2rM+4+z+TgKWNEpAvbpz8sL4gjqSGcJ87E0t/npmOhY35o2I+VS bM3rkhL4sTcknZFOm6T2ilmQIhGnWQVAsmrT/yXfdhHaHKXse6ioUbmCYLyCKwuA42B/Hhy1WM Epo= X-SBRS: 2.7 X-MesageID: 21039380 X-Ironport-Server: esa1.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.75,271,1589256000"; d="scan'208";a="21039380" Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace) To: Peter Zijlstra , Joerg Roedel CC: Andy Lutomirski , Joerg Roedel , "Dave Hansen" , Tom Lendacky , "Mike Stunes" , Dan Williams , "Dave Hansen" , "H. Peter Anvin" , Juergen Gross , Jiri Slaby , Kees Cook , kvm list , LKML , Thomas Hellstrom , Linux Virtualization , X86 ML , Sean Christopherson References: <20200428075512.GP30814@suse.de> <20200623110706.GB4817@hirez.programming.kicks-ass.net> <20200623113007.GH31822@suse.de> <20200623114818.GD4817@hirez.programming.kicks-ass.net> <20200623120433.GB14101@suse.de> <20200623125201.GG4817@hirez.programming.kicks-ass.net> <20200623134003.GD14101@suse.de> <20200623135916.GI4817@hirez.programming.kicks-ass.net> <20200623145344.GA117543@hirez.programming.kicks-ass.net> <20200623145914.GF14101@suse.de> <20200623152326.GL4817@hirez.programming.kicks-ass.net> From: Andrew Cooper Message-ID: <56af2f70-a1c6-aa64-006e-23f2f3880887@citrix.com> Date: Tue, 23 Jun 2020 16:39:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200623152326.GL4817@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Language: en-GB X-ClientProxiedBy: AMSPEX02CAS01.citrite.net (10.69.22.112) To AMSPEX02CL02.citrite.net (10.69.22.126) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/06/2020 16:23, Peter Zijlstra wrote: > On Tue, Jun 23, 2020 at 04:59:14PM +0200, Joerg Roedel wrote: >> On Tue, Jun 23, 2020 at 04:53:44PM +0200, Peter Zijlstra wrote: >>> +noinstr void idtentry_validate_ist(struct pt_regs *regs) >>> +{ >>> + if ((regs->sp & ~(EXCEPTION_STKSZ-1)) == >>> + (_RET_IP_ & ~(EXCEPTION_STKSZ-1))) >>> + die("IST stack recursion", regs, 0); >>> +} >> Yes, this is a start, it doesn't cover the case where the NMI stack is >> in-between, so I think you need to walk down regs->sp too. > That shouldn't be possible with the current code, I think. NMI; #MC; Anything which IRET but isn't fatal - #DB, or #BP from patching, #GP from *_safe(), etc; NMI Sure its a corner case, but did you hear that IST is evil? ~Andrew P.S. did you also hear that with Rowhammer, userspace has a nonzero quantity of control over generating #MC, depending on how ECC is configured on the platform.