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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 A864BC43441 for ; Wed, 10 Oct 2018 20:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68D412086E for ; Wed, 10 Oct 2018 20:16:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68D412086E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1727869AbeJKDkB (ORCPT ); Wed, 10 Oct 2018 23:40:01 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33000 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726911AbeJKDkA (ORCPT ); Wed, 10 Oct 2018 23:40:00 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A62EF3082E07; Wed, 10 Oct 2018 20:16:14 +0000 (UTC) Received: from treble (ovpn-124-83.rdu2.redhat.com [10.10.124.83]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C341482263; Wed, 10 Oct 2018 20:16:11 +0000 (UTC) Date: Wed, 10 Oct 2018 15:16:09 -0500 From: Josh Poimboeuf To: Steven Rostedt Cc: Andy Lutomirski , Peter Zijlstra , LKML , Linus Torvalds , Ingo Molnar , Andrew Morton , Thomas Gleixner , Masami Hiramatsu , Mathieu Desnoyers , Matthew Helsley , "Rafael J. Wysocki" , David Woodhouse , Paolo Bonzini , Jason Baron , Jiri Kosina , Ard Biesheuvel , Andrew Lutomirski Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function" Message-ID: <20181010201609.3zwvzpr3ulredpek@treble> References: <20181008155757.GC5663@hirez.programming.kicks-ass.net> <20181009021710.qwt5hpntyeps44h3@treble> <20181008235750.59da83ae@gandalf.local.home> <20181010175237.e7m3sldcu2maoqcq@treble> <20181010181605.arsyjxwdztztrjih@treble> <20181010183330.ootwmz6deazg2k2n@treble> <20181010145608.2094d254@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20181010145608.2094d254@gandalf.local.home> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Wed, 10 Oct 2018 20:16:15 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 10, 2018 at 02:56:08PM -0400, Steven Rostedt wrote: > On Wed, 10 Oct 2018 13:33:30 -0500 > Josh Poimboeuf wrote: > > > Re-reading your suggestion, I may have misunderstood what you're > > suggesting here, but I'm thinking about doing something like what you > > proposed earlier: > > > > GLOBAL(tramp) > > jmp *current_func(%rip) > > ENDPROC(tramp) > > > > That is, doing an indirect jump instead of the above direct jump, so > > that any previous references to the trampoline would still work (and it > > would also work during early boot). > > > > Though it should probably be a retpoline instead of an indirect jump. > > But do we care, as it only takes place during text_poke_bp() right? > > I don't think we need to worry about training trampoline branch > prediction that can only be hit when something enables the jump. Yeah, I guess it depends on if we'd expect anybody (or gcc) to get a function pointer to the trampoline itself. I can just create a warning for that in objtool. -- Josh