staging: android: ion: Zero CMA allocated memory

Since commit 204f672255c2 ("staging: android: ion: Use CMA APIs directly")
the CMA API is now used directly and therefore the allocated memory is no
longer automatically zeroed.

Explicitly zero CMA allocated memory to ensure that no data is exposed to
userspace.

Fixes: 204f672255c2 ("staging: android: ion: Use CMA APIs directly")
Signed-off-by: Liam Mark <lmark@codeaurora.org>
Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion_cma_heap.c

@@ -12,6 +12,7 @@
 #include <linux/err.h>
 #include <linux/cma.h>
 #include <linux/scatterlist.h>
+#include <linux/highmem.h>
 
 #include "ion.h"
 
@@ -42,6 +43,22 @@ static int ion_cma_allocate(struct ion_heap *heap, struct ion_buffer *buffer,
 	if (!pages)
 		return -ENOMEM;
 
+	if (PageHighMem(pages)) {
+		unsigned long nr_clear_pages = nr_pages;
+		struct page *page = pages;
+
+		while (nr_clear_pages > 0) {
+			void *vaddr = kmap_atomic(page);
+
+			memset(vaddr, 0, PAGE_SIZE);
+			kunmap_atomic(vaddr);
+			page++;
+			nr_clear_pages--;
+		}
+	} else {
+		memset(page_address(pages), 0, size);
+	}
+
 	table = kmalloc(sizeof(*table), GFP_KERNEL);
 	if (!table)
 		goto err;