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=-3.0 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 B82EFC43441 for ; Thu, 29 Nov 2018 13:11:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 82B3720863 for ; Thu, 29 Nov 2018 13:11:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 82B3720863 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 S1728466AbeK3AQs (ORCPT ); Thu, 29 Nov 2018 19:16:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40952 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728414AbeK3AQr (ORCPT ); Thu, 29 Nov 2018 19:16:47 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 68B9813AA2; Thu, 29 Nov 2018 13:11:28 +0000 (UTC) Received: from treble (ovpn-123-4.rdu2.redhat.com [10.10.123.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 71D07101962B; Thu, 29 Nov 2018 13:11:24 +0000 (UTC) Date: Thu, 29 Nov 2018 07:11:22 -0600 From: Josh Poimboeuf To: Peter Zijlstra Cc: 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: <20181129131122.wfceiqlnklruas6g@treble> References: <62188c62f6dda49ca2e20629ee8e5a62a6c0b500.1543200841.git.jpoimboe@redhat.com> <20181126160217.GR2113@hirez.programming.kicks-ass.net> <20181126171036.chcbmb35ygpxziub@treble> <20181126175624.bruqfbkngbucpvxr@treble> <20181126200801.GW2113@hirez.programming.kicks-ass.net> <20181126212628.4apztfazichxnt7r@treble> <20181127084330.GX2113@hirez.programming.kicks-ass.net> <20181129094210.GC2131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20181129094210.GC2131@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 29 Nov 2018 13:11:28 +0000 (UTC) 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 10:42:10AM +0100, Peter Zijlstra wrote: > On Wed, Nov 28, 2018 at 10:05:54PM -0800, Andy Lutomirski wrote: > > > >> +static void static_call_bp_handler(struct pt_regs *regs, void *_data) > > >> +{ > > >> + struct static_call_bp_data *data = _data; > > >> + > > >> + /* > > >> + * For inline static calls, push the return address on the stack so the > > >> + * "called" function will return to the location immediately after the > > >> + * call site. > > >> + * > > >> + * NOTE: This code will need to be revisited when kernel CET gets > > >> + * implemented. > > >> + */ > > >> + if (data->ret) { > > >> + regs->sp -= sizeof(long); > > >> + *(unsigned long *)regs->sp = data->ret; > > >> + } > > > > You can’t do this. Depending on the alignment of the old RSP, which > > is not guaranteed, this overwrites regs->cs. IRET goes boom. > > I don't get it; can you spell that out? I don't quite follow that either. Maybe Andy is referring to x86-32, for which regs->sp isn't actually saved: see kernel_stack_pointer(). This code is 64-bit only so that's not a concern. > The way I understand it is that we're at a location where a "E8 - Near > CALL" instruction should be, and thus RSP should be the regular kernel > stack, and the above simply does "PUSH ret", which is what that CALL > would've done too. Right. -- Josh