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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 6A37DC433E0 for ; Thu, 2 Jul 2020 20:59:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C43421534 for ; Thu, 2 Jul 2020 20:59:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726169AbgGBU7M (ORCPT ); Thu, 2 Jul 2020 16:59:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51276 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725937AbgGBU7M (ORCPT ); Thu, 2 Jul 2020 16:59:12 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2C22AC08C5C1 for ; Thu, 2 Jul 2020 13:59:12 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jr6IQ-004AR1-1t; Thu, 02 Jul 2020 20:59:02 +0000 Date: Thu, 2 Jul 2020 21:59:02 +0100 From: Al Viro To: Linus Torvalds Cc: Michael Ellerman , Christophe Leroy , Josh Poimboeuf , Peter Zijlstra , the arch/x86 maintainers , Linux Kernel Mailing List Subject: Re: objtool clac/stac handling change.. Message-ID: <20200702205902.GP2786714@ZenIV.linux.org.uk> References: <20200701184131.GI2786714@ZenIV.linux.org.uk> <20200701195914.GK2786714@ZenIV.linux.org.uk> <87lfk26nx4.fsf@mpe.ellerman.id.au> <20200702201755.GO2786714@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 02, 2020 at 01:32:34PM -0700, Linus Torvalds wrote: > Ugh, the above is bad anyway. > > It doesn't use _ASM_EXTABLE_UA, so it won't warn about the noncanonical cases. FWIW, the address is inside a sigframe we decided to build, so noncanonical addresses shouldn't occur in practice. > Yeah, it would need to be turned into a "jump out" instead of just "jump over". > > Which it damn well should do anyway., > > That code should be taken behind a shed and shot. It does so many > things wrong that it's not even funny. It shouldn't do stac/clac on > its own. > > At least it could use the "user_insn()" helper, which does it inside > the asm itself, has the right might_fault() marking (but not the > address check), and which can be trivially changed to have the fixup > jump be to after the "ASM_CLAC". I'm not sure it's the right solution in this case. Look at the call chain and the stuff done nearby (that __clear_user(), for example)... I'm not saying that this code is not awful - it certainly is. But it's not that simple, unfortunately ;-/