| Message ID | 20200330222309.5eTk9ZUJH%akpm@linux-foundation.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [merged] mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch removed from -mm tree | expand |
--- a/mm/sparse.c~mm-sparse-fix-kernel-crash-with-pfn_section_valid-check +++ a/mm/sparse.c @@ -781,6 +781,12 @@ static void section_deactivate(unsigned 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)
The patch titled Subject: mm/sparse: fix kernel crash with pfn_section_valid check has been removed from the -mm tree. Its filename was mm-sparse-fix-kernel-crash-with-pfn_section_valid-check.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> Subject: mm/sparse: fix kernel crash with pfn_section_valid check Fix 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. [aneesh.kumar@linux.ibm.com: add comment] Link: http://lkml.kernel.org/r/20200326133235.343616-1-aneesh.kumar@linux.ibm.comLink: http://lkml.kernel.org/r/20200325031914.107660-1-aneesh.kumar@linux.ibm.com Fixes: d41e2f3bd546 ("mm/hotplug: fix hot remove failure in SPARSEMEM|!VMEMMAP case") Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Reported-by: Sachin Sant <sachinp@linux.vnet.ibm.com> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com> Reviewed-by: Baoquan He <bhe@redhat.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com> Reviewed-by: Wei Yang <richard.weiyang@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Dan Williams <dan.j.williams@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/sparse.c | 6 ++++++ 1 file changed, 6 insertions(+)