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,URIBL_BLOCKED,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 47E4EC43381 for ; Sun, 17 Feb 2019 03:41:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 117732192C for ; Sun, 17 Feb 2019 03:41:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728152AbfBQDlc (ORCPT ); Sat, 16 Feb 2019 22:41:32 -0500 Received: from mail12.gandi.net ([217.70.182.73]:49195 "EHLO gandi.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726751AbfBQDlc (ORCPT ); Sat, 16 Feb 2019 22:41:32 -0500 Received: from khany.gandi.net (fob.gandi.net [217.70.181.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by gandi.net (Postfix) with ESMTPSA id 051EE160457; Sun, 17 Feb 2019 03:41:30 +0000 (UTC) Received: by khany.gandi.net (Postfix, from userid 1000) id E4770DD164B; Sun, 17 Feb 2019 03:41:21 +0000 (GMT) Date: Sun, 17 Feb 2019 03:41:21 +0000 From: Arthur Gautier To: Al Viro Cc: Andy Lutomirski , Thomas Gleixner , Jann Horn , the arch/x86 maintainers , Ingo Molnar , Borislav Petkov , kernel list , Pascal Bouchareine Subject: Re: [PATCH] x86: uaccess: fix regression in unsafe_get_user Message-ID: <20190217034121.bs3q3sgevexmdt3d@khany> References: <20190215235901.23541-1-baloo@gandi.net> <4F2693EA-1553-4F09-9475-781305540DBC@amacapital.net> <20190216234702.GP2217@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190216234702.GP2217@ZenIV.linux.org.uk> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 16, 2019 at 11:47:02PM +0000, Al Viro wrote: > On Sat, Feb 16, 2019 at 02:50:15PM -0800, Andy Lutomirski wrote: > > > What is the actual problem? We’re not actually demand-faulting this data, are we? Are we just overrunning the buffer because the from_user helpers are too clever? Can we fix it for real by having the fancy helpers do *aligned* loads so that they don’t overrun the buffer? Heck, this might be faster, too. > > Unaligned _stores_ are not any cheaper, and you'd get one hell of > extra arithmetics from trying to avoid both. Check something > like e.g. memcpy() on alpha, where you really have to keep all > accesses aligned, both on load and on store side. > > Can't we just pad the buffers a bit? Making sure that name_buf > and symlink_buf are _not_ followed by unmapped pages shouldn't > be hard. Both are allocated by kmalloc(), so... We cannot change alignment rules here. The input buffer string we're reading is coming from an cpio formated file and the format is defined by cpio(5). Nothing much we can do there I'm afraid. Input buffer is defined to be 4-byte aligned. -- \o/ Arthur G Gandi.net