Commit e492080e authored Nov 15, 2017 by Jaewon Kim Committed by Linus Torvalds Nov 15, 2017

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 f86e4271 ("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: eefa864b ("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 f86e4271, see above]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2bce774e

mm/page_ext.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -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);
		}

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