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=DKIM_INVALID,DKIM_SIGNED, 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 D9856C04EB9 for ; Thu, 29 Nov 2018 22:22:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 833BD20673 for ; Thu, 29 Nov 2018 22:22:25 +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="aJTNS1NE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 833BD20673 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 S1726525AbeK3J3Y (ORCPT ); Fri, 30 Nov 2018 04:29:24 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:57542 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726264AbeK3J3Y (ORCPT ); Fri, 30 Nov 2018 04:29:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=hpBaroZ5L6Yc/iydmxhSKSmTPJ0QW/yiM7cKr2sD8sI=; b=aJTNS1NE5CR+itjE+Zt7y+pRr f1FgIg6dLXyIzTBzRiq4xjopSrCHnYzUUhUUtm4MFFShAa/AXNFtWEiTU5vyDOhSC8vFpQogrIRvK L/+RrhocVI01RWQA4r+neqx2lH+JIWTQuGr2dLHa7L7MeNkGqovPGEBkBSLNfSLUJDw4AR36cI0uR 4MQHxxN3MvyGtOctIClBEOi23OsiiZ5GJrcRvpJFQfKwKv3Bo2Ri0OiiD6xXiomxHcOQrzSd278L3 V3xidU1puO7O0iZNGEyARVLBWqGkFokRCcMLvjimzSChPcACbBeqVa63tRRWnF2HauOyJlmOC8Vj/ b+kPz+YLw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gSUhG-00065c-TS; Thu, 29 Nov 2018 22:22:11 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 571A92029FD58; Thu, 29 Nov 2018 23:22:09 +0100 (CET) Date: Thu, 29 Nov 2018 23:22:09 +0100 From: Peter Zijlstra To: Josh Poimboeuf Cc: Andy Lutomirski , Andy Lutomirski , X86 ML , LKML , Ard Biesheuvel , Steven Rostedt , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Masami Hiramatsu , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov , julia@ni.com, jeyu@kernel.org, "H. Peter Anvin" Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 Message-ID: <20181129222209.GG11632@hirez.programming.kicks-ass.net> References: <20181129094210.GC2131@hirez.programming.kicks-ass.net> <20181129143853.GO2131@hirez.programming.kicks-ass.net> <20181129163342.tp5wlfcyiazwwyoh@treble> <20181129164914.GA9027@hirez.programming.kicks-ass.net> <0FDA053D-7ADC-4F42-AEA5-99DA155FCED0@amacapital.net> <20181129171050.iio53bw67fbiwzud@treble> <20181129220148.GD11632@hirez.programming.kicks-ass.net> <20181129221446.qb7znvt7zprlbz77@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181129221446.qb7znvt7zprlbz77@treble> 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 29, 2018 at 04:14:46PM -0600, Josh Poimboeuf wrote: > On Thu, Nov 29, 2018 at 11:01:48PM +0100, Peter Zijlstra wrote: > > On Thu, Nov 29, 2018 at 11:10:50AM -0600, Josh Poimboeuf wrote: > > > On Thu, Nov 29, 2018 at 08:59:31AM -0800, Andy Lutomirski wrote: > > > > > > (like pointing IP at a stub that retpolines to the target by reading > > > > the function pointer, a la the unoptimizable version), then okay, I > > > > guess, with only a small amount of grumbling. > > > > > > I tried that in v2, but Peter pointed out it's racy: > > > > > > https://lkml.kernel.org/r/20181126160217.GR2113@hirez.programming.kicks-ass.net > > > > Ah, but that is because it is a global shared trampoline. > > > > Each static_call has it's own trampoline; which currently reads > > something like: > > > > RETPOLINE_SAFE > > JMP *key > > > > which you then 'defuse' by writing an UD2 on. _However_, if you write > > that trampoline like: > > > > 1: RETPOLINE_SAFE > > JMP *key > > 2: CALL_NOSPEC *key > > RET > > > > and have the text_poke_bp() handler jump to 2 (a location you'll never > > reach when you enter at 1), it will in fact work I think. The trampoline > > is never modified and not shared between different static_call's. > > But after returning from the function to the trampoline, how does it > return from the trampoline to the call site? At that point there is no > return address on the stack. Oh, right, so that RET don't work. ARGH. Time to go sleep I suppose.