From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753387AbcKUITY (ORCPT ); Mon, 21 Nov 2016 03:19:24 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:55702 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751437AbcKUITX (ORCPT ); Mon, 21 Nov 2016 03:19:23 -0500 Date: Mon, 21 Nov 2016 09:16:44 +0100 (CET) From: Thomas Gleixner To: Peter Zijlstra cc: LKML , Ingo Molnar , x86@kernel.org, Borislav Petkov , Yinghai Lu Subject: Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle In-Reply-To: <20161120131002.GZ3117@twins.programming.kicks-ass.net> Message-ID: References: <20161119133816.633700010@linutronix.de> <20161119134017.732180441@linutronix.de> <20161120131002.GZ3117@twins.programming.kicks-ass.net> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 20 Nov 2016, Peter Zijlstra wrote: > On Sat, Nov 19, 2016 at 01:47:37PM -0000, Thomas Gleixner wrote: > > When entering idle, it's a good oportunity to verify that the TSC_ADJUST > > MSR has not been tampered with (BIOS hiding SMM cycles). If tampering is > > detected, emit a warning and restore it to the previous value. > > > +++ b/arch/x86/kernel/process.c > > @@ -277,6 +277,7 @@ void exit_idle(void) > > > > void arch_cpu_idle_enter(void) > > { > > + tsc_verify_tsc_adjust(); > > local_touch_nmi(); > > enter_idle(); > > } > > Doing a RDMSR on the idle path isn't going to be popular. That path is > already way too slow. Of course we can ratelimit that MSR read with jiffies, but do you have any better suggestion aside of doing it timer based? Thanks, tglx