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 7AF7CC10F29 for ; Mon, 9 Mar 2020 14:01:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 548A721D7E for ; Mon, 9 Mar 2020 14:01:56 +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="AKz+U+gF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727061AbgCIOBy (ORCPT ); Mon, 9 Mar 2020 10:01:54 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:39306 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727005AbgCIOBx (ORCPT ); Mon, 9 Mar 2020 10:01:53 -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=DtQS5O0hQQwBgslAAVUsLKrdeW4x55wzUHWwe5NBXGg=; b=AKz+U+gFd1aSjmGlOvFl3PMm/b V7ONgOBVPBl+LL+p0e6IvqZ9/ozi330UJkt1sWFzRdl7nbvTTG6DJiDiwV7J8/+QZ0YDwaRciyNJo Rro7rJqhN5dRSGYtmiMoE4wSmS/BVzgrY43a87z+SVWEff4i5mPG2HqgB8PnP/9i1l++pV2zidf3p ZyamoK9q1HN0wGGfvcRcbj/QJbtznsHgtLTgMg6hPhw6m9icokvLvNsTfxZAPfeXFM1NS7GRMP74d 4nx6vc9kYOYsJtD+Zww81MFJZSiNn1NZPXzZJR4s36B3StLeyITITlmZhNL9pAk5kT/kEgEv5NI9E G5Qme7rw==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jBIya-0002i3-QM; Mon, 09 Mar 2020 14:01:48 +0000 Date: Mon, 9 Mar 2020 07:01:48 -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: <20200309140148.GK31215@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> <20200308123616.GH31215@bombadil.infradead.org> <5E660863.2090104@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5E660863.2090104@samsung.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 09, 2020 at 06:12:03PM +0900, Jaewon Kim wrote: > On 2020년 03월 08일 21:36, Matthew Wilcox wrote: > > 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. > Although up to 10 times within 5 secs is not many, I think those log may remove > other important log in log buffer if it is the system which produces very few log. > In my Android phone device system, there seems to be much more kernel log though. I've never seen the logs on my android phone. All that a ratelimit is going to do is make the attacker be more patient. > > 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. > In Android phone device system, we cannot get sysadmin permission if it is built > for end user. And it is not easy to reproduce this symptom because it is an user's app. > > Anyway let me try pr_devel_ratelimited which is disabled by default. I hope this is > good enough. Additionally I moved the code from mm.h to mmap.c. https://source.android.com/devices/tech/debug/ftrace