[3.16.y-ckt,033/170] random: add and use memzero_explicit() for clearing data

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 71529e196b84..dde8da31dcae 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1076,8 +1076,8 @@  static void extract_buf(struct entropy_store *r, __u8 *out)
 	 * pool while mixing, and hash one final time.
 	 */
 	sha_transform(hash.w, extract, workspace);
-	memset(extract, 0, sizeof(extract));
-	memset(workspace, 0, sizeof(workspace));
+	memzero_explicit(extract, sizeof(extract));
+	memzero_explicit(workspace, sizeof(workspace));
 
 	/*
 	 * In case the hash function has some recognizable output
@@ -1089,7 +1089,7 @@  static void extract_buf(struct entropy_store *r, __u8 *out)
 	hash.w[2] ^= rol32(hash.w[2], 16);
 
 	memcpy(out, &hash, EXTRACT_SIZE);
-	memset(&hash, 0, sizeof(hash));
+	memzero_explicit(&hash, sizeof(hash));
 }
 
 /*
@@ -1146,7 +1146,7 @@  static ssize_t extract_entropy(struct entropy_store *r, void *buf,
 	}
 
 	/* Wipe data just returned from memory */
-	memset(tmp, 0, sizeof(tmp));
+	memzero_explicit(tmp, sizeof(tmp));
 
 	return ret;
 }
@@ -1188,7 +1188,7 @@  static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
 	}
 
 	/* Wipe data just returned from memory */
-	memset(tmp, 0, sizeof(tmp));
+	memzero_explicit(tmp, sizeof(tmp));
 
 	return ret;
 }
diff --git a/include/linux/string.h b/include/linux/string.h
index d36977e029af..3b42b3732da6 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -132,7 +132,7 @@  int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
 #endif
 
 extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
-			const void *from, size_t available);
+				       const void *from, size_t available);
 
 /**
  * strstarts - does @str start with @prefix?
@@ -144,7 +144,8 @@  static inline bool strstarts(const char *str, const char *prefix)
 	return strncmp(str, prefix, strlen(prefix)) == 0;
 }
 
-extern size_t memweight(const void *ptr, size_t bytes);
+size_t memweight(const void *ptr, size_t bytes);
+void memzero_explicit(void *s, size_t count);
 
 /**
  * kbasename - return the last part of a pathname.
diff --git a/lib/string.c b/lib/string.c
index 992bf30af759..3a3120452a1d 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -604,6 +604,22 @@  void *memset(void *s, int c, size_t count)
 EXPORT_SYMBOL(memset);
 #endif
 
+/**
+ * memzero_explicit - Fill a region of memory (e.g. sensitive
+ *		      keying data) with 0s.
+ * @s: Pointer to the start of the area.
+ * @count: The size of the area.
+ *
+ * memzero_explicit() doesn't need an arch-specific version as
+ * it just invokes the one of memset() implicitly.
+ */
+void memzero_explicit(void *s, size_t count)
+{
+	memset(s, 0, count);
+	OPTIMIZER_HIDE_VAR(s);
+}
+EXPORT_SYMBOL(memzero_explicit);
+
 #ifndef __HAVE_ARCH_MEMCPY
 /**
  * memcpy - Copy one area of memory to another