Commit 1c290f64 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds

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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: default avatarJérôme Glisse <jglisse@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Jerome Marchand <jmarchan@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 822cdd11
......@@ -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.
......
......@@ -1805,7 +1805,7 @@ 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;
......
......@@ -3096,7 +3096,7 @@ 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) {
/*
......
......@@ -466,6 +466,7 @@ 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);
}
}
......@@ -856,6 +857,10 @@ 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;
......@@ -866,6 +871,7 @@ 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;
}
......
......@@ -386,7 +386,9 @@ 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)))
......@@ -399,10 +401,10 @@ 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,
......
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