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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16497C76196 for ; Wed, 12 Apr 2023 00:15:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229533AbjDLAPl (ORCPT ); Tue, 11 Apr 2023 20:15:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51190 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229450AbjDLAPj (ORCPT ); Tue, 11 Apr 2023 20:15:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB69412B for ; Tue, 11 Apr 2023 17:15:38 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 519B86268F for ; Wed, 12 Apr 2023 00:15:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 752C0C433EF; Wed, 12 Apr 2023 00:15:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1681258537; bh=+4+26YeShVOy7ToR1aCgF4tHlAF/edewLYy1hsvDreo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=kPrR+RF5l0d0OtWpJ2ln+3K16rNYnnm9appIm0pPLkOrKrtPpX7uY9XtzB4q36I0w 9MUqIW/lhNIWqUu9X7f3GRzjNW9J0kADvH4gj3/q6g1AZt0KIOIsFfkn7OhLifbzTX thgoN+JVF7F6bcsWpbTmT+CTZ6NahIcSOXkrkVPw= Date: Tue, 11 Apr 2023 17:15:36 -0700 From: Andrew Morton To: Matthew Wilcox Cc: "xiaosong.ma" , Alexander Viro , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zhaoyang Huang , yuming.han@unisoc.com, ke.wang@unisoc.com Subject: Re: [PATCH V2] fs: perform the check when page without mapping but page->mapping contains junk or random bitscribble Message-Id: <20230411171536.2e53b4b7507304d5618aa24e@linux-foundation.org> In-Reply-To: References: <1681091102-31907-1-git-send-email-Xiaosong.Ma@unisoc.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 11 Apr 2023 13:16:18 +0100 Matthew Wilcox wrote: > On Mon, Apr 10, 2023 at 09:45:02AM +0800, xiaosong.ma wrote: > > perform the check in dump_mapping() to print warning info and avoid crash with invalid non-NULL page->mapping. > > For example, a panic with following backtraces show dump_page will show wrong info and panic when the bad page > > is non-NULL mapping and page->mapping is 0x80000000000. > > > > crash_arm64> bt > > PID: 232 TASK: ffffff80e8c2c340 CPU: 0 COMMAND: "Binder:232_2" > > #0 [ffffffc013e5b080] sysdump_panic_event$b2bce43a479f4f7762201bfee02d7889 at ffffffc0108d7c2c > > #1 [ffffffc013e5b0c0] atomic_notifier_call_chain at ffffffc010300228 > > #2 [ffffffc013e5b2c0] panic at ffffffc0102c926c > > #3 [ffffffc013e5b370] die at ffffffc010267670 > > #4 [ffffffc013e5b3a0] die_kernel_fault at ffffffc0102808a4 > > #5 [ffffffc013e5b3d0] __do_kernel_fault at ffffffc010280820 > > #6 [ffffffc013e5b410] do_bad_area at ffffffc01028059c > > #7 [ffffffc013e5b440] do_translation_fault$4df5decbea5d08a63349aa36f07426b2 at ffffffc0111149c8 > > #8 [ffffffc013e5b470] do_mem_abort at ffffffc0100a4488 > > #9 [ffffffc013e5b5e0] el1_ia at ffffffc0100a6c00 > > #10 [ffffffc013e5b5f0] __dump_page at ffffffc0104beecc > > This doesn't show a crash in dump_mapping(), it shows a crash in > __dump_page(). um, yes. But if page->mapping is corrupted, where does __dump_page() dereference it? The initial patch (https://lkml.kernel.org/r/1680587425-4683-1-git-send-email-Xiaosong.Ma@unisoc.com) prevented __dump_page() from calling dump_mapping() if page->mapping is bad, and that presumably fixed things. > > diff --git a/fs/inode.c b/fs/inode.c > > index f453eb5..c9021e5 100644 > > --- a/fs/inode.c > > +++ b/fs/inode.c > > @@ -564,7 +564,8 @@ void dump_mapping(const struct address_space *mapping) > > * If mapping is an invalid pointer, we don't want to crash > > * accessing it, so probe everything depending on it carefully. > > */ > > - if (get_kernel_nofault(host, &mapping->host) || > > + if (get_kernel_nofault(mapping, &mapping) || > > + get_kernel_nofault(host, &mapping->host) || > > This patch makes no sense. Essentially, you're saying > mapping = &mapping > which is obviously wrong. We're checking for mapping==junk, so this could be get_kernel_nofault(tmp, mapping) or go direct to copy_from_kernel_nofault(). We used to have a probe_kernel_address() for this... So confusion reigns. I think making dump_mapping() tolerant of a wild mapping pointer makes sense, but I don't think we actually know why the reporter's kernel crashed.