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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 33E17C10DCE for ; Sun, 8 Mar 2020 12:36:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 09795206D7 for ; Sun, 8 Mar 2020 12:36:31 +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="EoELTO+U" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726333AbgCHMgX (ORCPT ); Sun, 8 Mar 2020 08:36:23 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:42442 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726281AbgCHMgX (ORCPT ); Sun, 8 Mar 2020 08:36:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=IiyxS/rAQGOWd77kOuqz3QJtfeBB9AA2GpRhunGswrk=; b=EoELTO+UvK8cEeBI7Bq1jfWu3d ywOUjGWPVgdIUwlDwHNvAnz7A7jt7sRZESaRxJJYcCovlaqfDMi9D93ABJuzkCf9AawCJ5Y9F+smq yrc63tEYVdVPxNUB1bfT9mf+TLYlM83dgg3cnJWkX0hjFFFxhwkB+pfz1epXPfgu6Ml7mHXqS9Spg mAyYIkU7fVneJVUfeA3xN04kctD3HoRFMK3LF3RJ0ZMD8+woUpJnSRpOYiblMsuK5kks28grkLnQh U0W/z1MxHkm84qjJmknzYr8BtNuqQ0PDIFo+eGZvlKB8nF1zpYsBp3Xpq/1/IuN4aM84T0CuQEm92 /DgQQZtQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jAvAG-0001S6-TK; Sun, 08 Mar 2020 12:36:16 +0000 Date: Sun, 8 Mar 2020 05:36:16 -0700 From: Matthew Wilcox To: Jaewon Kim Cc: Andrew Morton , walken@google.com, bp@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, jaewon31.kim@gmail.com Subject: Re: [PATCH] mm: mmap: show vm_unmapped_area error log Message-ID: <20200308123616.GH31215@bombadil.infradead.org> References: <20200304030206.1706-1-jaewon31.kim@samsung.com> <5E605749.9050509@samsung.com> <20200305202443.8de3598558336b1d75afbba7@linux-foundation.org> <5E61EAB6.5080609@samsung.com> <20200307154744.acd523831b45efa8d0fc1dfa@linux-foundation.org> <20200308015802.GD31215@bombadil.infradead.org> <5E64C1D7.3000208@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5E64C1D7.3000208@samsung.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Mar 08, 2020 at 06:58:47PM +0900, Jaewon Kim wrote: > On 2020년 03월 08일 10:58, Matthew Wilcox wrote: > > On Sat, Mar 07, 2020 at 03:47:44PM -0800, Andrew Morton wrote: > >> On Fri, 6 Mar 2020 15:16:22 +0900 Jaewon Kim wrote: > >>> Even on 64 bit kernel, the mmap failure can happen for a 32 bit task. > >>> Virtual memory space shortage of a task on mmap is reported to userspace > >>> as -ENOMEM. It can be confused as physical memory shortage of overall > >>> system. > > But userspace can trigger this printk. We don't usually allow printks > > under those circumstances, even ratelimited. > Hello thank you your comment. > > Yes, userspace can trigger printk, but this was useful for to know why > a userspace task was crashed. There seems to be still many userspace > applications which did not check error of mmap and access invalid address. > > Additionally in my AARCH64 Android environment, display driver tries to > get userspace address to map its display memory. The display driver > report -ENOMEM from vm_unmapped_area and but also from GPU related > address space. > > Please let me know your comment again if this debug is now allowed > in that userspace triggered perspective. The scenario that worries us is an attacker being able to fill the log files and so also fill (eg) the /var partition. Once it's full, future kernel messages cannot be stored anywhere and so there will be no traces of their privilege escalation. Maybe a tracepoint would be a better idea? Usually they are disabled, but they can be enabled by a sysadmin to gain insight into why an application is crashing.