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Fri, 27 Mar 2020 05:42:14 -0400 X-MC-Unique: S-X6dZLUOzSOyk5LSxfybA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F02758014CD; Fri, 27 Mar 2020 09:42:11 +0000 (UTC) Received: from [10.36.112.108] (ovpn-112-108.ams2.redhat.com [10.36.112.108]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1C5E45C1D6; Fri, 27 Mar 2020 09:42:07 +0000 (UTC) Subject: Re: [PATCH v2] mm/sparse: Fix kernel crash with pfn_section_valid check To: "Aneesh Kumar K.V" , linux-mm@kvack.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, Sachin Sant , Baoquan He , Dan Williams , Pankaj Gupta , Michal Hocko , Wei Yang , Oscar Salvador , Mike Rapoport , stable@vger.kernel.org References: <20200326133235.343616-1-aneesh.kumar@linux.ibm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200326133235.343616-1-aneesh.kumar@linux.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Content-Transfer-Encoding: quoted-printable Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 26.03.20 14:32, Aneesh Kumar K.V wrote: > Fixes the below crash >=20 > 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=3D64K MMU=3DHash SMP NR_CPUS=3D2048 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 >=20 > The crash is due to NULL dereference at >=20 > test_bit(idx, ms->usage->subsection_map); due to ms->usage =3D NULL; in= pfn_section_valid() >=20 > With commit: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARS= EMEM|!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 >=20 > __section_mem_map_addr(__sec) + __pfn; > where >=20 > static inline struct page *__section_mem_map_addr(struct mem_section *s= ection) > { > unsigned long map =3D section->section_mem_map; > map &=3D SECTION_MAP_MASK; > return (struct page *)map; > } >=20 > 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. >=20 > static inline int pfn_valid(unsigned long pfn) > { > ... > return early_section(ms) || pfn_section_valid(ms, pfn); > } >=20 > where >=20 > static inline int pfn_section_valid(struct mem_section *ms, unsigned lo= ng pfn) > { > int idx =3D subsection_map_index(pfn); >=20 > return test_bit(idx, ms->usage->subsection_map); > } >=20 > Avoid this by clearing SECTION_HAS_MEM_MAP when mem_section->usage is f= reed. > For architectures like ppc64 where large pages are used for vmmemap map= ping (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 v= alid sections > within that mapping. Clearing the section valid bit before > depopulate_section_memap enables this. >=20 > 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(+) >=20 > 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 =3D NULL; > } > memmap =3D 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 s/return/returns/ > + * ms->usage array. maybe "(see pfn_section_valid())" > + */ > + ms->section_mem_map &=3D ~SECTION_HAS_MEM_MAP; --=20 Thanks, David / dhildenb