add page sanitization / verification

2 files changed, 32 insertions, 2 deletions

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 7fb31da45..41a50714f 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -7,6 +7,7 @@
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 #include <linux/hardirq.h>
+#include <linux/string.h>
 
 #include <asm/cacheflush.h>
 
@@ -189,6 +190,27 @@ static inline void clear_highpage(struct page *page)
 	kunmap_atomic(kaddr);
 }
 
+static inline void sanitize_highpage(struct page *page)
+{
+	void *kaddr;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	kaddr = kmap_atomic(page);
+	clear_page(kaddr);
+	kunmap_atomic(kaddr);
+	local_irq_restore(flags);
+}
+
+static inline void sanitize_highpage_verify(struct page *page)
+{
+	void *kaddr;
+
+	kaddr = kmap_atomic(page);
+	BUG_ON(memchr_inv(kaddr, 0, PAGE_SIZE));
+	kunmap_atomic(kaddr);
+}
+
 static inline void zero_user_segments(struct page *page,
 	unsigned start1, unsigned end1,
 	unsigned start2, unsigned end2)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 884c13be9..1139bde1d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -872,6 +872,8 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 	int i;
 	int bad = 0;
 
+	unsigned long index = 1UL << order;
+
 	trace_mm_page_free(page, order);
 	kmemcheck_free_shadow(page, order);
 	kasan_free_pages(page, order);
@@ -888,6 +890,10 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
 		debug_check_no_obj_freed(page_address(page),
 					   PAGE_SIZE << order);
 	}
+
+	for (; index; --index)
+		sanitize_highpage(page + index - 1);
+
 	arch_free_page(page, order);
 	kernel_map_pages(page, 1 << order, 0);
 
@@ -1096,6 +1102,8 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
 {
 	int i;
 
+	unsigned long index = 1UL << order;
+
 	for (i = 0; i < (1 << order); i++) {
 		struct page *p = page + i;
 		if (unlikely(check_new_page(p)))
@@ -1109,8 +1117,8 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
 	kernel_map_pages(page, 1 << order, 1);
 	kasan_alloc_pages(page, order);
 
-	if (gfp_flags & __GFP_ZERO)
-		prep_zero_page(page, order, gfp_flags);
+	for (; index; --index)
+		sanitize_highpage_verify(page + index - 1);
 
 	if (order && (gfp_flags & __GFP_COMP))
 		prep_compound_page(page, order);