>From cdb3d7e7f717f3e96ee97c4b0a29a745701bd813 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Tue, 18 Aug 2015 09:49:51 +1000 Subject: [PATCH] mm: sanitize page->mapping for tail pages We don't define meaning of page->mapping for tail pages. Currently it's always NULL, which can be inconsistent with head page and potentially lead to problems. Let's poison the pointer to catch all illigal uses. page_rmapping(), page_mapping() and page_anon_vma() are changed to look on head page. The only illegal use I've caught so far is __GPF_COMP pages from sound subsystem, mapped with PTEs. do_shared_fault() is changed to use page_rmapping() instead of direct access to fault_page->mapping. Signed-off-by: Kirill A. Shutemov Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Dave Hansen Cc: Mel Gorman Cc: Rik van Riel Cc: Vlastimil Babka Cc: Christoph Lameter Cc: Naoya Horiguchi Cc: Steve Capper Cc: "Aneesh Kumar K.V" Cc: Johannes Weiner Cc: Michal Hocko Cc: Jerome Marchand Signed-off-by: Andrew Morton --- include/linux/poison.h | 4 ++++ mm/huge_memory.c | 2 +- mm/memory.c | 2 +- mm/page_alloc.c | 6 ++++++ mm/util.c | 10 ++++++---- 5 files changed, 18 insertions(+), 6 deletions(-) diff --git a/include/linux/poison.h b/include/linux/poison.h index 2110a81c5e2a..7b2a7fcde6a3 100644 --- a/include/linux/poison.h +++ b/include/linux/poison.h @@ -32,6 +32,10 @@ /********** mm/debug-pagealloc.c **********/ #define PAGE_POISON 0xaa +/********** mm/page_alloc.c ************/ + +#define TAIL_MAPPING ((void *) 0x01014A11 + POISON_POINTER_DELTA) + /********** mm/slab.c **********/ /* * Magic nums for obj red zoning. diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 7ef15f8f8bf3..1a3accef0756 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1772,7 +1772,7 @@ static void __split_huge_page_refcount(struct page *page, */ page_tail->_mapcount = page->_mapcount; - BUG_ON(page_tail->mapping); + BUG_ON(page_tail->mapping != TAIL_MAPPING); page_tail->mapping = page->mapping; page_tail->index = page->index + i; diff --git a/mm/memory.c b/mm/memory.c index 6cd0b2160401..558ee16167d9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3087,7 +3087,7 @@ static int do_shared_fault(struct mm_struct *mm, struct vm_area_struct *vma, * pinned by vma->vm_file's reference. We rely on unlock_page()'s * release semantics to prevent the compiler from undoing this copying. */ - mapping = fault_page->mapping; + mapping = page_rmapping(fault_page); unlock_page(fault_page); if ((dirtied || vma->vm_ops->page_mkwrite) && mapping) { /* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d752298a9e48..adefa3ad8e3e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -470,6 +470,7 @@ void prep_compound_page(struct page *page, unsigned int order) for (i = 1; i < nr_pages; i++) { struct page *p = page + i; set_page_count(p, 0); + p->mapping = TAIL_MAPPING; set_compound_head(p, page); } } @@ -855,6 +856,10 @@ static int free_tail_pages_check(struct page *head_page, struct page *page) ret = 0; goto out; } + if (page->mapping != TAIL_MAPPING) { + bad_page(page, "corrupted mapping in tail page", 0); + goto out; + } if (unlikely(!PageTail(page))) { bad_page(page, "PageTail not set", 0); goto out; @@ -865,6 +870,7 @@ static int free_tail_pages_check(struct page *head_page, struct page *page) } ret = 0; out: + page->mapping = NULL; clear_compound_head(page); return ret; } diff --git a/mm/util.c b/mm/util.c index 68ff8a5361e7..0c7f65e7ef5e 100644 --- a/mm/util.c +++ b/mm/util.c @@ -355,7 +355,9 @@ struct anon_vma *page_anon_vma(struct page *page) struct address_space *page_mapping(struct page *page) { - unsigned long mapping; + struct address_space *mapping; + + page = compound_head(page); /* This happens if someone calls flush_dcache_page on slab page */ if (unlikely(PageSlab(page))) @@ -368,10 +370,10 @@ struct address_space *page_mapping(struct page *page) return swap_address_space(entry); } - mapping = (unsigned long)page->mapping; - if (mapping & PAGE_MAPPING_FLAGS) + mapping = page->mapping; + if ((unsigned long)mapping & PAGE_MAPPING_FLAGS) return NULL; - return page->mapping; + return mapping; } int overcommit_ratio_handler(struct ctl_table *table, int write, -- 2.5.0