security: don't treat structure as an array of struct hlist_head

The initialization of "security_hook_heads" is done by casting it to
another structure pointer type, and treating it as an array of "struct
hlist_head" objects. This requires an exception be made in "randstruct",
because otherwise it will emit an error, reducing the effectiveness of
the hardening technique.

Instead of using a cast, initialize the individual struct hlist_head
elements in security_hook_heads explicitly. This removes the need for
the cast and randstruct exception.
Signed-off-by: Bill Wendling <morbo@google.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220407175930.471870-1-morbo@google.com

scripts/gcc-plugins/randomize_layout_plugin.c

@@ -52,8 +52,6 @@ static const struct whitelist_entry whitelist[] = {
 	{ "net/unix/af_unix.c", "unix_skb_parms", "char" },
 	/* big_key payload.data struct splashing */
 	{ "security/keys/big_key.c", "path", "void *" },
-	/* walk struct security_hook_heads as an array of struct hlist_head */
-	{ "security/security.c", "hlist_head", "security_hook_heads" },
 	{ }
 };
 

security/security.c

@@ -365,13 +365,12 @@ static void __init ordered_lsm_init(void)
 
 int __init early_security_init(void)
 {
-	int i;
-	struct hlist_head *list = (struct hlist_head *) &security_hook_heads;
 	struct lsm_info *lsm;
 
-	for (i = 0; i < sizeof(security_hook_heads) / sizeof(struct hlist_head);
-	     i++)
-		INIT_HLIST_HEAD(&list[i]);
+#define LSM_HOOK(RET, DEFAULT, NAME, ...) \
+	INIT_HLIST_HEAD(&security_hook_heads.NAME);
+#include "linux/lsm_hook_defs.h"
+#undef LSM_HOOK
 
 	for (lsm = __start_early_lsm_info; lsm < __end_early_lsm_info; lsm++) {
 		if (!lsm->enabled)