elf: Partially initialize ld.so after static dlopen (bug 20802)

After static dlopen, a copy of ld.so is loaded into the inner
namespace, but that copy is not initialized at all.  Some
architectures run into serious problems as result, which is why the
_dl_var_init mechanism was invented.  With libpthread moving into
libc and parts into ld.so, more architectures impacted, so it makes
sense to switch to a generic mechanism which performs the partial
initialization.

As a result, getauxval now works after static dlopen (bug 20802).

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

dlfcn/tststatic5.c

@@ -25,14 +25,9 @@
    mapped from a static executable.
 
    On targets that support different page sizes, the kernel communicates
-   the size currently in use via the auxiliary vector.  This vector is
-   available to initial startup, but not any DSOs loaded later on.  As
-   static executables do not export their symbols a DSO cannot access
-   the value obtained by initial startup and the value therefore has to
-   be passed on to the DSO and stored within its data area explicitly.
-   This is performed by a call to DL_STATIC_INIT that is defined in a
-   target-dependent way, and that on variable page size targets stores
-   it in the GLRO(dl_pagesize) variable of the DSO's dynamic linker.  */
+   the size currently in use via the auxiliary vector.  The auxiliary
+   vector and HWCAP/HWCAP2 bits are copied across the static dlopen
+   boundary in __rtld_static_init.  */
 static int
 do_test (void)
 {

elf/Makefile

@@ -25,7 +25,7 @@ headers		= elf.h bits/elfclass.h link.h bits/link.h
 routines	= $(all-dl-routines) dl-support dl-iteratephdr \
 		  dl-addr dl-addr-obj enbl-secure dl-profstub \
 		  dl-origin dl-libc dl-sym dl-sysdep dl-error \
-		  dl-reloc-static-pie libc_early_init
+		  dl-reloc-static-pie libc_early_init rtld_static_init
 
 # The core dynamic linking functions are in libc for the static and
 # profiled libraries.
@@ -60,7 +60,7 @@ all-dl-routines = $(dl-routines) $(sysdep-dl-routines)
 # But they are absent from the shared libc, because that code is in ld.so.
 elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \
 		    dl-sysdep dl-exception dl-reloc-static-pie \
-		    thread_gscope_wait
+		    thread_gscope_wait rtld_static_init
 
 # ld.so uses those routines, plus some special stuff for being the program
 # interpreter and operating independent of libc.
@@ -161,7 +161,7 @@ tests-static-normal := tst-leaks1-static tst-array1-static tst-array5-static \
 	       tst-tlsalign-static tst-tlsalign-extern-static \
 	       tst-linkall-static tst-env-setuid tst-env-setuid-tunables \
 	       tst-single_threaded-static tst-single_threaded-pthread-static \
-	       tst-dst-static
+	       tst-dst-static tst-getauxval-static
 
 tests-static-internal := tst-tls1-static tst-tls2-static \
 	       tst-ptrguard1-static tst-stackguard1-static \
@@ -346,6 +346,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		libmarkermod3-1 libmarkermod3-2 libmarkermod3-3 \
 		libmarkermod4-1 libmarkermod4-2 libmarkermod4-3 libmarkermod4-4 \
 		tst-tls20mod-bad tst-tls21mod tst-dlmopen-dlerror-mod \
+		tst-auxvalmod \
 
 # Most modules build with _ISOMAC defined, but those filtered out
 # depend on internal headers.
@@ -1942,3 +1943,7 @@ $(objpfx)tst-tls20.out: $(objpfx)tst-tls20mod-bad.so \
 $(objpfx)tst-tls21: $(libdl) $(shared-thread-library)
 $(objpfx)tst-tls21.out: $(objpfx)tst-tls21mod.so
 $(objpfx)tst-tls21mod.so: $(tst-tls-many-dynamic-modules:%=$(objpfx)%.so)
+
+$(objpfx)tst-getauxval-static: $(common-objpfx)dlfcn/libdl.a
+$(objpfx)tst-getauxval-static.out: $(objpfx)tst-auxvalmod.so
+tst-getauxval-static-ENV = LD_LIBRARY_PATH=$(objpfx):$(common-objpfx)

elf/dl-open.c

@@ -35,6 +35,7 @@
 #include <libc-internal.h>
 #include <array_length.h>
 #include <libc-early-init.h>
+#include <gnu/lib-names.h>
 
 #include <dl-dst.h>
 #include <dl-prop.h>
@@ -590,8 +591,20 @@ dl_open_worker (void *a)
   /* So far, so good.  Now check the versions.  */
   for (unsigned int i = 0; i < new->l_searchlist.r_nlist; ++i)
     if (new->l_searchlist.r_list[i]->l_real->l_versions == NULL)
-      (void) _dl_check_map_versions (new->l_searchlist.r_list[i]->l_real,
-				     0, 0);
+      {
+	struct link_map *map = new->l_searchlist.r_list[i]->l_real;
+	_dl_check_map_versions (map, 0, 0);
+#ifndef SHARED
+	/* During static dlopen, check if ld.so has been loaded.
+	   Perform partial initialization in this case.  This must
+	   come after the symbol versioning initialization in
+	   _dl_check_map_versions.  */
+	if (map->l_info[DT_SONAME] != NULL
+	    && strcmp (((const char *) D_PTR (map, l_info[DT_STRTAB])
+			+ map->l_info[DT_SONAME]->d_un.d_val), LD_SO) == 0)
+	  __rtld_static_init (map);
+#endif
+      }
 
 #ifdef SHARED
   /* Auditing checkpoint: we have added all objects.  */

elf/rtld_static_init.c

@@ -0,0 +1,56 @@
+/* Partial initialization of ld.so loaded via static dlopen.
+   Copyright (C) 2021 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/>.  */
+
+#include <assert.h>
+
+/* Very special case: This object is built into the static libc, but
+   must know the layout of _rtld_global_ro.  */
+#define SHARED
+#include <ldsodefs.h>
+
+#include <rtld_static_init.h>
+
+void
+__rtld_static_init (struct link_map *map)
+{
+  const ElfW(Sym) *sym
+    = _dl_lookup_direct (map, "_rtld_global_ro",
+                         0x9f28436a, /* dl_new_hash output.  */
+                         "GLIBC_PRIVATE",
+                         0x0963cf85); /* _dl_elf_hash output.  */
+  assert (sym != NULL);
+  struct rtld_global_ro *dl = DL_SYMBOL_ADDRESS (map, sym);
+
+  /* Perform partial initialization here.  Note that this runs before
+     ld.so is relocated, so only members initialized without
+     relocations can be written here.  */
+#ifdef HAVE_AUX_VECTOR
+  extern __typeof (dl->_dl_auxv) _dl_auxv attribute_hidden;
+  dl->_dl_auxv = _dl_auxv;
+  extern __typeof (dl->_dl_clktck) _dl_clktck attribute_hidden;
+  dl->_dl_clktck = _dl_clktck;
+#endif
+  extern __typeof (dl->_dl_hwcap) _dl_hwcap attribute_hidden;
+  dl->_dl_hwcap = _dl_hwcap;
+  extern __typeof (dl->_dl_hwcap2) _dl_hwcap2 attribute_hidden;
+  dl->_dl_hwcap2 = _dl_hwcap2;
+  extern __typeof (dl->_dl_pagesize) _dl_pagesize attribute_hidden;
+  dl->_dl_pagesize = _dl_pagesize;
+
+  __rtld_static_init_arch (map, dl);
+}

elf/tst-auxvalmod.c

@@ -0,0 +1,29 @@
+/* Wrapper for getauxval testing.
+   Copyright (C) 2021 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/>.  */
+
+#include <errno.h>
+#include <sys/auxv.h>
+
+unsigned long
+getauxval_wrapper (unsigned long type, int *errnop)
+{
+  errno = *errnop;
+  unsigned long result = getauxval (type);
+  *errnop = errno;
+  return result;
+}

elf/tst-getauxval-static.c

@@ -0,0 +1,66 @@
+/* Test getauxval from a dynamic library after static dlopen.
+   Copyright (C) 2021 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/>.  */
+
+#include <dlfcn.h>
+#include <errno.h>
+#include <stdio.h>
+#include <support/check.h>
+#include <support/xdlfcn.h>
+#include <sys/auxv.h>
+
+unsigned long getauxval_wrapper (unsigned long type, int *errnop);
+
+static int
+do_test (void)
+{
+  unsigned long outer_random = getauxval (AT_RANDOM);
+  if (outer_random == 0)
+    FAIL_UNSUPPORTED ("getauxval does not support AT_RANDOM");
+
+  unsigned long missing_auxv_type;
+  for (missing_auxv_type = AT_RANDOM + 1; ; ++missing_auxv_type)
+    {
+      errno = 0;
+      if (getauxval (missing_auxv_type) == 0 && errno != 0)
+        {
+          TEST_COMPARE (errno, ENOENT);
+          break;
+        }
+    }
+  printf ("info: first missing type: %lu\n", missing_auxv_type);
+
+  void *handle = xdlopen ("tst-auxvalmod.so", RTLD_LAZY);
+  void *ptr = xdlsym (handle, "getauxval_wrapper");
+
+  __typeof__ (getauxval_wrapper) *wrapper = ptr;
+  int inner_errno = 0;
+  unsigned long inner_random = wrapper (AT_RANDOM, &inner_errno);
+  TEST_COMPARE (outer_random, inner_random);
+
+  inner_errno = 0;
+  TEST_COMPARE (wrapper (missing_auxv_type, &inner_errno), 0);
+  TEST_COMPARE (inner_errno, ENOENT);
+
+  TEST_COMPARE (getauxval (AT_HWCAP), wrapper (AT_HWCAP, &inner_errno));
+  TEST_COMPARE (getauxval (AT_HWCAP2), wrapper (AT_HWCAP2, &inner_errno));
+
+  xdlclose (handle);
+  return 0;
+}
+
+#include <support/test-driver.c>

sysdeps/generic/ldsodefs.h

@@ -1313,6 +1313,13 @@ dl_init_static_tls (struct link_map *map)
 #endif
 }
 
+#ifndef SHARED
+/* Called before relocating ld.so during static dlopen.  This can be
+   used to partly initialize the dormant ld.so copy in the static
+   dlopen namespace.  */
+void __rtld_static_init (struct link_map *map) attribute_hidden;
+#endif
+
 /* Return true if the ld.so copy in this namespace is actually active
    and working.  If false, the dl_open/dlfcn hooks have to be used to
    call into the outer dynamic linker (which happens after static

sysdeps/generic/rtld_static_init.h

@@ -0,0 +1,24 @@
+/* Partial initialization of ld.so loaded via static dlopen.  Generic helper.
+   Copyright (C) 2021 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/>.  */
+
+static inline void
+__rtld_static_init_arch (struct link_map *map, struct rtld_global_ro *dl)
+{
+  /* The generic helper does not perform any additional
+     initialization.  */
+}