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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 34071FC6182 for ; Fri, 14 Sep 2018 13:09:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E31F221476 for ; Fri, 14 Sep 2018 13:09:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="T1xFGiNm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E31F221476 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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 S1728073AbeINSYQ (ORCPT ); Fri, 14 Sep 2018 14:24:16 -0400 Received: from merlin.infradead.org ([205.233.59.134]:41142 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726905AbeINSYQ (ORCPT ); Fri, 14 Sep 2018 14:24:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=NF29tKOzYCiURtg4l6vs2wbn0JpKa4nWYshkG8p/AJs=; b=T1xFGiNm/wC6y9OWIc0HMg4HG wJcVuJ5hFiP+bE/ICETitQQhwEn3W1YbOqi/0wqLNJROb0B7r3mjQmM7xgI5AX/Gq3iXBRo9Fy+Hw 2Nh++CEGikarvaha1glOPx/DjcktyX4s5nkSp4kL/eHratF31cjZxvjSJrvNQkJ4t+PldqwRY1tKG zHUVEmGjDstjClLZGsuPfxt5pb/SZhXkKUMPmnUtNLzgrnFRP3EEs7Nh3epW+JzyvEt22sqXQewbf //VeT3PARv0WINsYt+3FJo0xukJqWtby9A1gj1CVtghrQ8SLqZhOG+pbI7argCvwmA5GqHDgvV1St 5DgV/aK1g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g0nqk-0002ah-0s; Fri, 14 Sep 2018 13:09:30 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DA74A202B2E3B; Fri, 14 Sep 2018 15:09:27 +0200 (CEST) Date: Fri, 14 Sep 2018 15:09:27 +0200 From: Peter Zijlstra To: Florian Weimer Cc: Thomas Gleixner , LKML , Andy Lutomirski , x86@kernel.org, Matt Rickard , Stephen Boyd , John Stultz , "K. Y. Srinivasan" , Vitaly Kuznetsov , devel@linuxdriverproject.org, virtualization@lists.linux-foundation.org, Paolo Bonzini , Arnd Bergmann , Juergen Gross Subject: Re: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI support Message-ID: <20180914130927.GK24124@hirez.programming.kicks-ass.net> References: <20180914125006.349747096@linutronix.de> <2f723b28-8f81-4b02-861c-42f756a8825a@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f723b28-8f81-4b02-861c-42f756a8825a@redhat.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 14, 2018 at 02:56:46PM +0200, Florian Weimer wrote: > On 09/14/2018 02:50 PM, Thomas Gleixner wrote: > > Matt attempted to add CLOCK_TAI support to the VDSO clock_gettime() > > implementation, which extended the clockid switch case and added yet > > another slightly different copy of the same code. > > > > Especially the extended switch case is problematic as the compiler tends to > > generate a jump table which then requires to use retpolines. > > Does vDSO code really have to use retpolines? It's in userspace, after all. Userspace is equally susceptible to spectre-v2. Ideally we'd recompile world with retpoline, but given the amount of inline asm in say things like openssl and similar projects, validating that there are indeed no indirect calls/jumps left is nontrivial. There are currently pending patches to otherwise address user-user spectre-v2 attacks.