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From:   Igor Stoppa <igor.stoppa@huawei.com>
To:     <david@fromorbit.com>, <willy@infradead.org>,
        <keescook@chromium.org>, <mhocko@kernel.org>
CC:     <labbott@redhat.com>, <linux-security-module@vger.kernel.org>,
        <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        <kernel-hardening@lists.openwall.com>,
        Igor Stoppa <igor.stoppa@huawei.com>
Subject: [PATCH 3/7] struct page: add field for vm_struct
Date:   Wed, 28 Feb 2018 22:06:16 +0200
Message-ID: <20180228200620.30026-4-igor.stoppa@huawei.com>
In-Reply-To: <20180228200620.30026-1-igor.stoppa@huawei.com>
References: <20180228200620.30026-1-igor.stoppa@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@huawei.com>
---
 include/linux/mm_types.h | 1 +
 mm/vmalloc.c             | 2 ++
 2 files changed, 3 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 ebff729cc956..61a1ca22b0f6 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);
 		}
 
@@ -1705,6 +1706,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
 			area->nr_pages = i;
 			goto fail;
 		}
+		page->area = area;
 		area->pages[i] = page;
 		if (gfpflags_allow_blocking(gfp_mask|highmem_mask))
 			cond_resched();
-- 
2.14.1