Do not allow to load ET_DYN object with DF_1_PIE flag set.

Linkers are supposed to mark PIE binaries with DF_1_PIE, such binary
cannot be correctly and usefully loaded neither by dlopen(3) nor as a
dependency of other object.  For instance, we cannot do anything
useful with COPY relocations, among other things.

Glibc already added similar restriction.

Requested and reviewed by:	emaste
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D25086

libexec/rtld-elf/rtld.c

@@ -1370,6 +1370,8 @@ digest_dynamic1(Obj_Entry *obj, int early, const Elf_Dyn **dyn_rpath,
 		    obj->z_interpose = true;
 		if (dynp->d_un.d_val & DF_1_NODEFLIB)
 		    obj->z_nodeflib = true;
+		if (dynp->d_un.d_val & DF_1_PIE)
+		    obj->z_pie = true;
 	    break;
 
 	default:
@@ -2580,6 +2582,10 @@ do_load_object(int fd, const char *name, char *path, struct stat *sbp,
     obj->path = path;
     if (!digest_dynamic(obj, 0))
 	goto errp;
+    if (obj->z_pie) {
+	_rtld_error("Cannot load PIE binary %s as dso", obj->path);
+	goto errp;
+    }
     dbg("%s valid_hash_sysv %d valid_hash_gnu %d dynsymcount %d", obj->path,
 	obj->valid_hash_sysv, obj->valid_hash_gnu, obj->dynsymcount);
     if (obj->z_noopen && (flags & (RTLD_LO_DLOPEN | RTLD_LO_TRACE)) ==

libexec/rtld-elf/rtld.h

@@ -257,6 +257,7 @@ typedef struct Struct_Obj_Entry {
     bool z_interpose : 1;	/* Interpose all objects but main */
     bool z_nodeflib : 1;	/* Don't search default library path */
     bool z_global : 1;		/* Make the object global */
+    bool z_pie : 1;		/* Object proclaimed itself PIE executable */
     bool static_tls : 1;	/* Needs static TLS allocation */
     bool static_tls_copied : 1;	/* Needs static TLS copying */
     bool ref_nodel : 1;		/* Refcount increased to prevent dlclose */