kernel-hardening - [PATCH 3/7] struct page: add field for vm

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Date: Fri, 23 Feb 2018 16:48:03 +0200
From: Igor Stoppa <igor.stoppa@...wei.com>
To: <david@...morbit.com>, <willy@...radead.org>, <keescook@...omium.org>,
	<mhocko@...nel.org>
CC: <labbott@...hat.com>, <linux-security-module@...r.kernel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<kernel-hardening@...ts.openwall.com>, Igor Stoppa <igor.stoppa@...wei.com>
Subject: [PATCH 3/7] struct page: add field for vm_struct

When a page is used for virtual memory, it is often necessary to obtain
a handler to the corresponding vm_struct, which refers to the virtually
continuous area generated when invoking vmalloc.

The struct page has a "mapping" field, which can be re-used, to store a
pointer to the parent area.

This will avoid more expensive searches, later on.

Signed-off-by: Igor Stoppa <igor.stoppa@...wei.com>
---
 include/linux/mm_types.h | 1 +
 mm/vmalloc.c             | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fd1af6b9591d..c3a4825e10c0 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -84,6 +84,7 @@ struct page {
 		void *s_mem;			/* slab first object */
 		atomic_t compound_mapcount;	/* first tail page */
 		/* page_deferred_list().next	 -- second tail page */
+		struct vm_struct *area;
 	};
 
 	/* Second double word */
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 673942094328..14d99ed22397 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1536,6 +1536,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
 			struct page *page = area->pages[i];
 
 			BUG_ON(!page);
+			page->area = NULL;
 			__free_pages(page, 0);
 		}
 
@@ -1744,6 +1745,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 			const void *caller)
 {
 	struct vm_struct *area;
+	unsigned int i;
 	void *addr;
 	unsigned long real_size = size;
 
@@ -1769,6 +1771,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
 
 	kmemleak_vmalloc(area, size, gfp_mask);
 
+	for (i = 0; i < area->nr_pages; i++)
+		area->pages[i]->area = area;
+
 	return addr;
 
 fail:
-- 
2.14.1

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