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 <kirill.shutemov@xxxxxxxxxxxxxxx>
---
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 317e16de09e5..76c3b6c38c16 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 244c852d565c..65ab7858bbcc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1836,7 +1836,7 @@ 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 caecc64301e9..3bd465a6fa0d 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 321a91747949..9bcfd70b1eb8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -473,6 +473,7 @@ 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);
}
}
@@ -864,6 +865,10 @@ 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;
@@ -874,6 +879,7 @@ 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 9af1c12b310c..902b65a43899 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,
--
2.5.1
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