From: Jaewon Kim jaewon31.kim@samsung.com Subject: mm/page_ext.c: check if page_ext is not prepared

online_page_ext() and page_ext_init() allocate page_ext for each section, but they do not allocate if the first PFN is !pfn_present(pfn) or !pfn_valid(pfn). Then section->page_ext remains as NULL. lookup_page_ext checks NULL only if CONFIG_DEBUG_VM is enabled. For a valid PFN, __set_page_owner will try to get page_ext through lookup_page_ext. Without CONFIG_DEBUG_VM lookup_page_ext will misuse NULL pointer as value 0. This incurrs invalid address access.

This is the panic example when PFN 0x100000 is not valid but PFN 0x13FC00 is being used for page_ext. section->page_ext is NULL, get_entry returned invalid page_ext address as 0x1DFA000 for a PFN 0x13FC00.

To avoid this panic, CONFIG_DEBUG_VM should be removed so that page_ext will be checked at all times.

<1>[ 11.618085] Unable to handle kernel paging request at virtual address 01dfa014 <1>[ 11.618140] pgd = ffffffc0c6dc9000 <1>[ 11.618174] [01dfa014] *pgd=0000000000000000, *pud=0000000000000000 <4>[ 11.618240] ------------[ cut here ]------------ <2>[ 11.618278] Kernel BUG at ffffff80082371e0 [verbose debug info unavailable] <0>[ 11.618338] Internal error: Oops: 96000045 [#1] PREEMPT SMP <4>[ 11.618381] Modules linked in: <4>[ 11.618524] task: ffffffc0c6ec9180 task.stack: ffffffc0c6f40000 <4>[ 11.618569] PC is at __set_page_owner+0x48/0x78 <4>[ 11.618607] LR is at __set_page_owner+0x44/0x78 <4>[ 11.626025] [<ffffff80082371e0>] __set_page_owner+0x48/0x78 <4>[ 11.626071] [<ffffff80081df9f0>] get_page_from_freelist+0x880/0x8e8 <4>[ 11.626118] [<ffffff80081e00a4>] __alloc_pages_nodemask+0x14c/0xc48 <4>[ 11.626165] [<ffffff80081e610c>] __do_page_cache_readahead+0xdc/0x264 <4>[ 11.626214] [<ffffff80081d8824>] filemap_fault+0x2ac/0x550 <4>[ 11.626259] [<ffffff80082e5cf8>] ext4_filemap_fault+0x3c/0x58 <4>[ 11.626305] [<ffffff800820a2f8>] __do_fault+0x80/0x120 <4>[ 11.626347] [<ffffff800820eb4c>] handle_mm_fault+0x704/0xbb0 <4>[ 11.626393] [<ffffff800809ba70>] do_page_fault+0x2e8/0x394 <4>[ 11.626437] [<ffffff8008080be4>] do_mem_abort+0x88/0x124

Pre-4.7 kernels also need f86e427197 ("mm: check the return value of lookup_page_ext for all call sites").

Link: http://lkml.kernel.org/r/20171107094131.14621-1-jaewon31.kim@samsung.com Fixes: eefa864b701d ("mm/page_ext: resurrect struct page extending code for debugging") Signed-off-by: Jaewon Kim jaewon31.kim@samsung.com Acked-by: Michal Hocko mhocko@suse.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Minchan Kim minchan@kernel.org Cc: Joonsoo Kim js1304@gmail.com Cc: stable@vger.kernel.org [depends on f86e427197, see above] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_ext.c | 4 ---- 1 file changed, 4 deletions(-)

diff -puN mm/page_ext.c~mm-page_ext-check-if-page_ext-is-not-prepared mm/page_ext.c --- a/mm/page_ext.c~mm-page_ext-check-if-page_ext-is-not-prepared +++ a/mm/page_ext.c @@ -125,7 +125,6 @@ struct page_ext *lookup_page_ext(struct struct page_ext *base;

base = NODE_DATA(page_to_nid(page))->node_page_ext; -#if defined(CONFIG_DEBUG_VM) /* * The sanity checks the page allocator does upon freeing a * page can reach here before the page_ext arrays are @@ -134,7 +133,6 @@ struct page_ext *lookup_page_ext(struct */ if (unlikely(!base)) return NULL; -#endif index = pfn - round_down(node_start_pfn(page_to_nid(page)), MAX_ORDER_NR_PAGES); return get_entry(base, index); @@ -199,7 +197,6 @@ struct page_ext *lookup_page_ext(struct { unsigned long pfn = page_to_pfn(page); struct mem_section *section = __pfn_to_section(pfn); -#if defined(CONFIG_DEBUG_VM) /* * The sanity checks the page allocator does upon freeing a * page can reach here before the page_ext arrays are @@ -208,7 +205,6 @@ struct page_ext *lookup_page_ext(struct */ if (!section->page_ext) return NULL; -#endif return get_entry(section->page_ext, pfn); }

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