The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e492080e640c2d1235ddf3441cae634cfffef7e1 Mon Sep 17 00:00:00 2001

From: Jaewon Kim jaewon31.kim@samsung.com Date: Wed, 15 Nov 2017 17:39:07 -0800 Subject: [PATCH] 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.

Unable to handle kernel paging request at virtual address 01dfa014 ------------[ cut here ]------------ Kernel BUG at ffffff80082371e0 [verbose debug info unavailable] Internal error: Oops: 96000045 [#1] PREEMPT SMP Modules linked in: PC is at __set_page_owner+0x48/0x78 LR is at __set_page_owner+0x44/0x78 __set_page_owner+0x48/0x78 get_page_from_freelist+0x880/0x8e8 __alloc_pages_nodemask+0x14c/0xc48 __do_page_cache_readahead+0xdc/0x264 filemap_fault+0x2ac/0x550 ext4_filemap_fault+0x3c/0x58 __do_fault+0x80/0x120 handle_mm_fault+0x704/0xbb0 do_page_fault+0x2e8/0x394 do_mem_abort+0x88/0x124

Pre-4.7 kernels also need commit f86e4271978b ("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 Signed-off-by: Linus Torvalds torvalds@linux-foundation.org

diff --git a/mm/page_ext.c b/mm/page_ext.c index 4f0367d472c4..2c16216c29b6 100644 --- a/mm/page_ext.c +++ b/mm/page_ext.c @@ -125,7 +125,6 @@ struct page_ext *lookup_page_ext(struct page *page) 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 page *page) */ 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 page *page) { 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 page *page) */ if (!section->page_ext) return NULL; -#endif return get_entry(section->page_ext, pfn); }