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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 1CCD9C2D0EC for ; Thu, 26 Mar 2020 16:05:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E291F208E0 for ; Thu, 26 Mar 2020 16:05:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="dqwJ3vnz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727056AbgCZQFC (ORCPT ); Thu, 26 Mar 2020 12:05:02 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:55550 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726296AbgCZQFC (ORCPT ); Thu, 26 Mar 2020 12:05:02 -0400 Received: by mail-wm1-f66.google.com with SMTP id z5so7037044wml.5; Thu, 26 Mar 2020 09:05:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=jWhswxN9HQxV0nCCW/ijA/LKBxQbID7mVe37gnQPitw=; b=dqwJ3vnz7U9zrvNqIgM2MDrOPkPRJntsqjaUCmayPiZXmgOePCAwQg68NmMORGrzvp 7VjndEdtlEs+VOWlBovC+Na0ujFud/i42W2fKEqCuQXj3iBBtyYtgBYZXtyakEPHwrh9 nOtf7SN6f/bFWtl9cyF7qnc0F+rFjpBMyceLyPWmVaOzRb+90/p7c+HCv/FQTk5l2iDt +MRM4AimWwn4DUObLtVRGdbBTCWmcPeeO/hEUHji22d3rK9fKhFQoEtWHn1IpGWP9TYZ SSxxE5u4B1fvpCxrojfEMZoq9rnzFJrO5l8/DeLc4q1/3UPYTxlZywbgf8d6zwqoNIIn aWnA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=jWhswxN9HQxV0nCCW/ijA/LKBxQbID7mVe37gnQPitw=; b=FMZ4zH6lKFNlqi3cvPsB4P7u1rpHCZ88SgwqcqP4JAbQP/WXnQON4GrSVOkDUyxd0t EyBGbBM0hrKtLR2Ol255dL3MPgsH0MXyMr/9S9m2Wcbe0wAHBntOuimlbs0oMrz+O9DG MhiawK7KETQqkyjn3K6dzcbpxxSJIy0B3GCLL3G+zBax70pnJL3/APEuYCHeytreCt62 gHsCcb6905RQaa//YOU8Zwji/lv+qMoXz+teGKuj3r5NcvSLqV1eEXyz6eLglktlTixI IjHUQ6IJ4rHsuVyf0G6vaj+UYke7s1wWClyDMkG35sKfvVobgBitKuvinX5Cd5OlPIX0 G9cg== X-Gm-Message-State: ANhLgQ3ZOWmVo/VhGn9zowYtxJG4ThPvm1m8GLMpdXrFLXZ1vcmlX6P8 ROPX2ME2nEhE6ecvkMbTBKYNIkJV1gBZFMz7hhI= X-Google-Smtp-Source: ADFU+vtaOxhcczxMAOz9StdZVZLixx/TTBbQdMAPFVdjZvzd+1/+U/20Y3/RjtNPR7fcn8ajcWhgZEzfyIZ2bGxXIZI= X-Received: by 2002:a1c:5506:: with SMTP id j6mr623256wmb.127.1585238699504; Thu, 26 Mar 2020 09:04:59 -0700 (PDT) MIME-Version: 1.0 References: <20200326133235.343616-1-aneesh.kumar@linux.ibm.com> In-Reply-To: <20200326133235.343616-1-aneesh.kumar@linux.ibm.com> From: Pankaj Gupta Date: Thu, 26 Mar 2020 17:04:47 +0100 Message-ID: Subject: Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, Sachin Sant , Baoquan He , Dan Williams , David Hildenbrand , Michal Hocko , Wei Yang , Oscar Salvador , Mike Rapoport , stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org > > Fixes the below crash > > BUG: Kernel NULL pointer dereference on read at 0x00000000 > Faulting instruction address: 0xc000000000c3447c > Oops: Kernel access of bad area, sig: 11 [#1] > LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries > CPU: 11 PID: 7519 Comm: lt-ndctl Not tainted 5.6.0-rc7-autotest #1 > ... > NIP [c000000000c3447c] vmemmap_populated+0x98/0xc0 > LR [c000000000088354] vmemmap_free+0x144/0x320 > Call Trace: > section_deactivate+0x220/0x240 > __remove_pages+0x118/0x170 > arch_remove_memory+0x3c/0x150 > memunmap_pages+0x1cc/0x2f0 > devm_action_release+0x30/0x50 > release_nodes+0x2f8/0x3e0 > device_release_driver_internal+0x168/0x270 > unbind_store+0x130/0x170 > drv_attr_store+0x44/0x60 > sysfs_kf_write+0x68/0x80 > kernfs_fop_write+0x100/0x290 > __vfs_write+0x3c/0x70 > vfs_write+0xcc/0x240 > ksys_write+0x7c/0x140 > system_call+0x5c/0x68 > > The crash is due to NULL dereference at > > test_bit(idx, ms->usage->subsection_map); due to ms->usage = NULL; in pfn_section_valid() > > With commit: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > section_mem_map is set to NULL after depopulate_section_mem(). This > was done so that pfn_page() can work correctly with kernel config that disables > SPARSEMEM_VMEMMAP. With that config pfn_to_page does > > __section_mem_map_addr(__sec) + __pfn; > where > > static inline struct page *__section_mem_map_addr(struct mem_section *section) > { > unsigned long map = section->section_mem_map; > map &= SECTION_MAP_MASK; > return (struct page *)map; > } > > Now with SPASEMEM_VMEMAP enabled, mem_section->usage->subsection_map is used to > check the pfn validity (pfn_valid()). Since section_deactivate release > mem_section->usage if a section is fully deactivated, pfn_valid() check after > a subsection_deactivate cause a kernel crash. > > static inline int pfn_valid(unsigned long pfn) > { > ... > return early_section(ms) || pfn_section_valid(ms, pfn); > } > > where > > static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) > { > int idx = subsection_map_index(pfn); > > return test_bit(idx, ms->usage->subsection_map); > } > > Avoid this by clearing SECTION_HAS_MEM_MAP when mem_section->usage is freed. > For architectures like ppc64 where large pages are used for vmmemap mapping (16MB), > a specific vmemmap mapping can cover multiple sections. Hence before a vmemmap > mapping page can be freed, the kernel needs to make sure there are no valid sections > within that mapping. Clearing the section valid bit before > depopulate_section_memap enables this. > > Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") > Reported-by: Sachin Sant > Tested-by: Sachin Sant > Cc: Baoquan He > Cc: Michael Ellerman > Cc: Dan Williams > Cc: Pankaj Gupta > Cc: David Hildenbrand > Cc: Michal Hocko > Cc: Wei Yang > Cc: Oscar Salvador > Cc: Mike Rapoport > Cc: > Signed-off-by: Aneesh Kumar K.V > --- > mm/sparse.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/sparse.c b/mm/sparse.c > index aadb7298dcef..65599e8bd636 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -781,6 +781,12 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages, > ms->usage = NULL; > } > memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr); > + /* > + * Mark the section invalid so that valid_section() > + * return false. This prevents code from dereferencing > + * ms->usage array. > + */ > + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP; > } > > if (section_is_early && memmap) > -- Agree with Michal, comment for clearing the section would be nicer. Fix looks good to me. Acked-by: Pankaj Gupta > 2.25.1 >