elf: Move vDSO setup to rtld (BZ#24967)

This patch moves the vDSO setup from libc to loader code, just after
the vDSO link_map setup.  For static case the initialization
is moved to _dl_non_dynamic_init instead.

Instead of using the mangled pointer, the vDSO data is set as
attribute_relro (on _rtld_global_ro for shared or _dl_vdso_* for
static).  It is read-only even with partial relro.

It fixes BZ#24967 now that the vDSO pointer is setup earlier than
malloc interposition is called.

Also, vDSO calls should not be a problem for static dlopen as
indicated by BZ#20802.  The vDSO pointer would be zero-initialized
and the syscall will be issued instead.

Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
arm-linux-gnueabihf, powerpc64le-linux-gnu, powerpc64-linux-gnu,
powerpc-linux-gnu, s390x-linux-gnu, sparc64-linux-gnu, and
sparcv9-linux-gnu.  I also run some tests on mips.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

sysdeps/generic/dl-vdso-setup.c

@@ -0,0 +1 @@
+/* Empty.  */

sysdeps/generic/dl-vdso-setup.h

@@ -0,0 +1,28 @@
+/* ELF symbol initialization functions for VDSO objects.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _DL_VDSO_INIT_H
+#define _DL_VDSO_INIT_H
+
+/* Initialize the VDSO functions pointers.  */
+static inline void __attribute__ ((always_inline))
+setup_vdso_pointers (void)
+{
+}
+
+#endif

sysdeps/generic/dl-vdso.h

@@ -0,0 +1,30 @@
+/* ELF symbol resolve functions for VDSO objects.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef _DL_VDSO_H
+#define _DL_VDSO_H	1
+
+/* Function for resolving symbols in the VDSO link map.  Return the
+   address of the vdso symbol NAME. */
+static inline void *
+dl_vdso_vsym (const char *name)
+{
+  return NULL;
+}
+
+#endif

sysdeps/generic/ldsodefs.h

@@ -608,6 +608,12 @@ struct rtld_global_ro
   /* At startup time we set up the normal DSO data structure for it,
      and this points to it.  */
   EXTERN struct link_map *_dl_sysinfo_map;
+
+# define PROCINFO_DECL
+# ifndef PROCINFO_CLASS
+#  define PROCINFO_CLASS EXTERN
+# endif
+# include <dl-vdso-setup.c>
 #endif
 
   /* Mask for more hardware capabilities that are available on some