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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 CE875C43441 for ; Thu, 22 Nov 2018 10:10:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9102720866 for ; Thu, 22 Nov 2018 10:10:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="TD6rNKnK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9102720866 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=alien8.de 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 S2393887AbeKVUtA (ORCPT ); Thu, 22 Nov 2018 15:49:00 -0500 Received: from mail.skyhub.de ([5.9.137.197]:33020 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393869AbeKVUtA (ORCPT ); Thu, 22 Nov 2018 15:49:00 -0500 Received: from zn.tnic (p200300EC2BDC9100898E5A1DF8FAB135.dip0.t-ipconnect.de [IPv6:2003:ec:2bdc:9100:898e:5a1d:f8fa:b135]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id A73771EC0AD8; Thu, 22 Nov 2018 11:10:13 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1542881413; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=i2GhZdFswSy8O5JtZOi+k0vsm1MtJprLiBowyrddS0Y=; b=TD6rNKnKHoXrmHTysyAThI4smgm1mhGSd76iXiHlqd6QgJ2DJlSeD4OiA2nyqjIL90hzgx RkKHzz5DY1jRoGs+Zk8zrQNahuVu0I7cCM7nR1Szu2bdtuR+Eu1nyzunZeMJTasNWvcd7n 7cOpRVEqJNI6IBr2zroJqsWszowksQk= Date: Thu, 22 Nov 2018 11:10:07 +0100 From: Borislav Petkov To: Peter Zijlstra Cc: Thomas Gleixner , Tom Lendacky , LKML , x86@kernel.org, Andy Lutomirski , Linus Torvalds , Jiri Kosina , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Dave Stewart , Kees Cook Subject: Re: [patch 15/24] x86/speculation: Add command line control for indirect branch speculation Message-ID: <20181122101007.GB10365@zn.tnic> References: <20181121201430.559770965@linutronix.de> <20181121201723.764150349@linutronix.de> <20181121234312.GI27559@zn.tnic> <20181122091858.GJ2131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181122091858.GJ2131@hirez.programming.kicks-ass.net> 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 Thu, Nov 22, 2018 at 10:18:58AM +0100, Peter Zijlstra wrote: > Right; that retpoline + IBPB case is one that came up earlier when we > talked about this stuff. The IBPB also helps against app2app BTB ASLR > attacks. So even if you have userspace retpoline, you might still want > IBPB. > > But yes, this should be relatively straight forward to allow/fix with > the proposed code. So I got some feedback from AMD that IBPB on context switch has a small perf impact and they wouldn't mind it being enabled by default considering that it provides protection against a lot of attack scenarios. Basically, what the recommendation says. But if we go and do opt-in, then they're fine with it being off by default if we decide to do it so in the kernel. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.