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=-3.8 required=3.0 tests=BAYES_00, 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 4840CC433DB for ; Wed, 3 Mar 2021 16:07:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B623964ED0 for ; Wed, 3 Mar 2021 16:07:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B623964ED0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 0E0688D017C; Wed, 3 Mar 2021 11:07:17 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 091648D0157; Wed, 3 Mar 2021 11:07:17 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E4CA68D017C; Wed, 3 Mar 2021 11:07:16 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0217.hostedemail.com [216.40.44.217]) by kanga.kvack.org (Postfix) with ESMTP id CC8898D0157 for ; Wed, 3 Mar 2021 11:07:16 -0500 (EST) Received: from smtpin10.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 9048D8249980 for ; Wed, 3 Mar 2021 16:07:16 +0000 (UTC) X-FDA: 77879042472.10.494C904 Received: from out03.mta.xmission.com (out03.mta.xmission.com [166.70.13.233]) by imf09.hostedemail.com (Postfix) with ESMTP id F014D6000122 for ; Wed, 3 Mar 2021 16:07:08 +0000 (UTC) Received: from in02.mta.xmission.com ([166.70.13.52]) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lHU1i-007Exf-4t; Wed, 03 Mar 2021 09:07:06 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=fess.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lHU1g-00FvUx-IR; Wed, 03 Mar 2021 09:07:05 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Ilya Lipnitskiy Cc: Linux-MM , Linux Kernel Mailing List , linux-fsdevel , Kees Cook , Christoph Hellwig , Linus Torvalds References: Date: Wed, 03 Mar 2021 10:07:04 -0600 In-Reply-To: (Ilya Lipnitskiy's message of "Wed, 3 Mar 2021 07:55:56 -0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1lHU1g-00FvUx-IR;;;mid=;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+5w/aqDaOXboiiwZQ4f+WJ2beqidtd74s= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: exec error: BUG: Bad rss-counter X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) X-Stat-Signature: 49wu7ax9dun36atn417pjx1wgbb9jy4a X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F014D6000122 Received-SPF: none (xmission.com>: No applicable sender policy available) receiver=imf09; identity=mailfrom; envelope-from=""; helo=out03.mta.xmission.com; client-ip=166.70.13.233 X-HE-DKIM-Result: none/none X-HE-Tag: 1614787628-4236 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Ilya Lipnitskiy writes: > On Wed, Mar 3, 2021 at 7:50 AM Eric W. Biederman wrote: >> >> Ilya Lipnitskiy writes: >> >> > On Tue, Mar 2, 2021 at 11:37 AM Eric W. Biederman wrote: >> >> >> >> Ilya Lipnitskiy writes: >> >> >> >> > On Mon, Mar 1, 2021 at 12:43 PM Eric W. Biederman wrote: >> >> >> >> >> >> Ilya Lipnitskiy writes: >> >> >> >> >> >> > Eric, All, >> >> >> > >> >> >> > The following error appears when running Linux 5.10.18 on an embedded >> >> >> > MIPS mt7621 target: >> >> >> > [ 0.301219] BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:1 >> >> >> > >> >> >> > Being a very generic error, I started digging and added a stack dump >> >> >> > before the BUG: >> >> >> > Call Trace: >> >> >> > [<80008094>] show_stack+0x30/0x100 >> >> >> > [<8033b238>] dump_stack+0xac/0xe8 >> >> >> > [<800285e8>] __mmdrop+0x98/0x1d0 >> >> >> > [<801a6de8>] free_bprm+0x44/0x118 >> >> >> > [<801a86a8>] kernel_execve+0x160/0x1d8 >> >> >> > [<800420f4>] call_usermodehelper_exec_async+0x114/0x194 >> >> >> > [<80003198>] ret_from_kernel_thread+0x14/0x1c >> >> >> > >> >> >> > So that's how I got to looking at fs/exec.c and noticed quite a few >> >> >> > changes last year. Turns out this message only occurs once very early >> >> >> > at boot during the very first call to kernel_execve. current->mm is >> >> >> > NULL at this stage, so acct_arg_size() is effectively a no-op. >> >> >> >> >> >> If you believe this is a new error you could bisect the kernel >> >> >> to see which change introduced the behavior you are seeing. >> >> >> >> >> >> > More digging, and I traced the RSS counter increment to: >> >> >> > [<8015adb4>] add_mm_counter_fast+0xb4/0xc0 >> >> >> > [<80160d58>] handle_mm_fault+0x6e4/0xea0 >> >> >> > [<80158aa4>] __get_user_pages.part.78+0x190/0x37c >> >> >> > [<8015992c>] __get_user_pages_remote+0x128/0x360 >> >> >> > [<801a6d9c>] get_arg_page+0x34/0xa0 >> >> >> > [<801a7394>] copy_string_kernel+0x194/0x2a4 >> >> >> > [<801a880c>] kernel_execve+0x11c/0x298 >> >> >> > [<800420f4>] call_usermodehelper_exec_async+0x114/0x194 >> >> >> > [<80003198>] ret_from_kernel_thread+0x14/0x1c >> >> >> > >> >> >> > In fact, I also checked vma_pages(bprm->vma) and lo and behold it is set to 1. >> >> >> > >> >> >> > How is fs/exec.c supposed to handle implied RSS increments that happen >> >> >> > due to page faults when discarding the bprm structure? In this case, >> >> >> > the bug-generating kernel_execve call never succeeded, it returned -2, >> >> >> > but I didn't trace exactly what failed. >> >> >> >> >> >> Unless I am mistaken any left over pages should be purged by exit_mmap >> >> >> which is called by mmput before mmput calls mmdrop. >> >> > Good to know. Some more digging and I can say that we hit this error >> >> > when trying to unmap PFN 0 (is_zero_pfn(pfn) returns TRUE, >> >> > vm_normal_page returns NULL, zap_pte_range does not decrement >> >> > MM_ANONPAGES RSS counter). Is my understanding correct that PFN 0 is >> >> > usable, but special? Or am I totally off the mark here? >> >> >> >> It would be good to know if that is the page that get_user_pages_remote >> >> returned to copy_string_kernel. The zero page that is always zero, >> >> should never be returned when a writable mapping is desired. >> > >> > Indeed, pfn 0 is returned from get_arg_page: (page is 0x809cf000, >> > page_to_pfn(page) is 0) and it is the same page that is being freed and not >> > refcounted in mmput/zap_pte_range. Confirmed with good old printk. Also, >> > ZERO_PAGE(0)==0x809fc000 -> PFN 5120. >> > >> > I think I have found the problem though, after much digging and thanks to all >> > the information provided. init_zero_pfn() gets called too late (after >> > the call to >> > is_zero_pfn(0) from mmput returns true), until then zero_pfn == 0, and after, >> > zero_pfn == 5120. Boom. >> > >> > So PFN 0 is special, but only for a little bit, enough for something >> > on my system >> > to call kernel_execve :) >> > >> > Question: is my system not supposed to be calling kernel_execve this >> > early or does >> > init_zero_pfn() need to happen earlier? init_zero_pfn is currently a >> > core_initcall. >> >> Looking quickly it seems that init_zero_pfn() is in mm/memory.c and is >> common for both mips and x86. Further it appears init_zero_pfn() has >> been that was since 2009 a13ea5b75964 ("mm: reinstate ZERO_PAGE"). >> >> Given the testing that x86 gets and that nothing like this has been >> reported it looks like whatever driver is triggering the kernel_execve >> is doing something wrong. > >> >> Because honestly. If the zero page isn't working there is not a chance >> that anything in userspace is working so it is clearly much too early. >> >> I suspect there is some driver that is initialized very early that is >> doing something that looks innocuous (like triggering a hotplug event) >> and that happens to cause a call_usermode_helper which then calls >> kernel_execve. > I will investigate the offenders more closely. However, I do not > notice this behavior on the same system based on the 5.4 kernel. Is it > possible that last year's exec changes have exposed this issue? Not > blaming exec at all, just making sure I understand the problem better. Only in the sense that copy_strings_kernel does less work than "set_fs(KERNEL_DS); copy_strings; set_fs(USER_DS);" Nothing huge was changed in exec but lots was moved around so that it was clearer what is happening, and so that hacks like set_fs could be removed. Eric