elf: Issue audit la_objopen for vDSO

The vDSO is is listed in the link_map chain, but is never the subject of
an la_objopen call.  A new internal flag __RTLD_VDSO is added that
acts as __RTLD_OPENEXEC to allocate the required 'struct auditstate'
extra space for the 'struct link_map'.

The return value from the callback is currently ignored, since there
is no PLT call involved by glibc when using the vDSO, neither the vDSO
are exported directly.

Checked on x86_64-linux-gnu, i686-linux-gnu, and aarch64-linux-gnu.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

elf/Makefile

@@ -232,6 +232,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-dl-is_dso tst-ro-dynamic \
 	 tst-audit18 \
 	 tst-audit19b \
+	 tst-audit22 \
 	 tst-rtld-run-static \
 #	 reldep9
 tests-internal += loadtest unload unload2 circleload1 \
@@ -382,6 +383,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		tst-auditmod19a \
 		tst-auditmod19b \
 		tst-audit19bmod \
+		tst-auditmod22 \
 
 # Most modules build with _ISOMAC defined, but those filtered out
 # depend on internal headers.
@@ -1594,6 +1596,9 @@ $(objpfx)tst-audit19b.out: $(objpfx)tst-auditmod19b.so
 $(objpfx)tst-audit19b: $(objpfx)tst-audit19bmod.so
 tst-audit19b-ARGS = -- $(host-test-program-cmd)
 
+$(objpfx)tst-audit22.out: $(objpfx)tst-auditmod22.so
+tst-audit22-ARGS = -- $(host-test-program-cmd)
+
 # tst-sonamemove links against an older implementation of the library.
 LDFLAGS-tst-sonamemove-linkmod1.so = \
   -Wl,--version-script=tst-sonamemove-linkmod1.map \

elf/dl-object.c

@@ -59,16 +59,19 @@ _dl_new_object (char *realname, const char *libname, int type,
 {
 #ifdef SHARED
   unsigned int naudit;
-  if (__glibc_unlikely ((mode & __RTLD_OPENEXEC) != 0))
+  if (__glibc_unlikely ((mode & (__RTLD_OPENEXEC | __RTLD_VDSO)) != 0))
     {
-      assert (type == lt_executable);
-      assert (nsid == LM_ID_BASE);
+      if (mode & __RTLD_OPENEXEC)
+	{
+	  assert (type == lt_executable);
+	  assert (nsid == LM_ID_BASE);
 
-      /* Ignore the specified libname for the main executable.  It is
-	 only known with an explicit loader invocation.  */
-      libname = "";
+	  /* Ignore the specified libname for the main executable.  It is
+	     only known with an explicit loader invocation.  */
+	  libname = "";
+	}
 
-      /* We create the map for the executable before we know whether
+      /* We create the map for the executable and vDSO before we know whether
 	 we have auditing libraries and if yes, how many.  Assume the
 	 worst.  */
       naudit = DL_NNS;

elf/rtld.c

@@ -1912,6 +1912,12 @@ dl_main (const ElfW(Phdr) *phdr,
       assert (i == npreloads);
     }
 
+#ifdef NEED_DL_SYSINFO_DSO
+  /* Now that the audit modules are opened, call la_objopen for the vDSO.  */
+  if (GLRO(dl_sysinfo_map) != NULL)
+    _dl_audit_objopen (GLRO(dl_sysinfo_map), LM_ID_BASE);
+#endif
+
   /* Load all the libraries specified by DT_NEEDED entries.  If LD_PRELOAD
      specified some libraries to load, these are inserted before the actual
      dependencies in the executable's searchlist for symbol resolution.  */

elf/setup-vdso.h

@@ -30,7 +30,7 @@ setup_vdso (struct link_map *main_map __attribute__ ((unused)),
      We just want our data structures to describe it as if we had just
      mapped and relocated it normally.  */
   struct link_map *l = _dl_new_object ((char *) "", "", lt_library, NULL,
-				       0, LM_ID_BASE);
+				       __RTLD_VDSO, LM_ID_BASE);
   if (__glibc_likely (l != NULL))
     {
       l->l_phdr = ((const void *) GLRO(dl_sysinfo_dso)

elf/tst-audit22.c

@@ -0,0 +1,124 @@
+/* Check DTAUDIT and vDSO interaction.
+   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 <getopt.h>
+#include <limits.h>
+#include <inttypes.h>
+#include <string.h>
+#include <stdlib.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <support/xstdio.h>
+#include <support/support.h>
+#include <sys/auxv.h>
+
+static int restart;
+#define CMDLINE_OPTIONS \
+  { "restart", no_argument, &restart, 1 },
+
+static uintptr_t vdso_addr;
+
+static int
+handle_restart (void)
+{
+  fprintf (stderr, "vdso: %p\n", (void*) vdso_addr);
+  return 0;
+}
+
+static uintptr_t
+parse_address (const char *str)
+{
+  void *r;
+  TEST_COMPARE (sscanf (str, "%p\n", &r), 1);
+  return (uintptr_t) r;
+}
+
+static inline bool
+startswith (const char *str, const char *pre)
+{
+  size_t lenpre = strlen (pre);
+  size_t lenstr = strlen (str);
+  return lenstr >= lenpre && memcmp (pre, str, lenpre) == 0;
+}
+
+static int
+do_test (int argc, char *argv[])
+{
+  vdso_addr = getauxval (AT_SYSINFO_EHDR);
+  if (vdso_addr == 0)
+    FAIL_UNSUPPORTED ("getauxval (AT_SYSINFO_EHDR) returned 0");
+
+  /* We must have either:
+     - One our fource parameters left if called initially:
+       + path to ld.so         optional
+       + "--library-path"      optional
+       + the library path      optional
+       + the application name  */
+  if (restart)
+    return handle_restart ();
+
+  char *spargv[9];
+  int i = 0;
+  for (; i < argc - 1; i++)
+    spargv[i] = argv[i + 1];
+  spargv[i++] = (char *) "--direct";
+  spargv[i++] = (char *) "--restart";
+  spargv[i] = NULL;
+
+  setenv ("LD_AUDIT", "tst-auditmod22.so", 0);
+  struct support_capture_subprocess result
+    = support_capture_subprogram (spargv[0], spargv);
+  support_capture_subprocess_check (&result, "tst-audit22", 0, sc_allow_stderr);
+
+  /* The respawned process should always print the vDSO address (otherwise it
+     will fails as unsupported).  However, on some architectures the audit
+     module might see the vDSO with l_addr being 0, meaning a fixed mapping
+     (linux-gate.so).  In this case we don't check its value against
+     AT_SYSINFO_EHDR one.  */
+  uintptr_t vdso_process = 0;
+  bool vdso_audit_found = false;
+  uintptr_t vdso_audit = 0;
+
+  FILE *out = fmemopen (result.err.buffer, result.err.length, "r");
+  TEST_VERIFY (out != NULL);
+  char *buffer = NULL;
+  size_t buffer_length = 0;
+  while (xgetline (&buffer, &buffer_length, out))
+    {
+      if (startswith (buffer, "vdso: "))
+	vdso_process = parse_address (buffer + strlen ("vdso: "));
+      else if (startswith (buffer, "vdso found: "))
+	{
+	  vdso_audit = parse_address (buffer + strlen ("vdso found: "));
+          vdso_audit_found = true;
+	}
+    }
+
+  TEST_COMPARE (vdso_audit_found, true);
+  if (vdso_audit != 0)
+    TEST_COMPARE (vdso_process, vdso_audit);
+
+  free (buffer);
+  xfclose (out);
+
+  return 0;
+}
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>

elf/tst-auditmod22.c

@@ -0,0 +1,51 @@
+/* Check DTAUDIT and vDSO interaction.
+   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 <link.h>
+#include <inttypes.h>
+#include <stdbool.h>
+#include <string.h>
+#include <stdio.h>
+#include <sys/auxv.h>
+
+static inline bool
+startswith (const char *str, const char *pre)
+{
+  size_t lenpre = strlen (pre);
+  size_t lenstr = strlen (str);
+  return lenstr < lenpre ? false : memcmp (pre, str, lenpre) == 0;
+}
+
+unsigned int
+la_version (unsigned int version)
+{
+  return LAV_CURRENT;
+}
+
+unsigned int
+la_objopen (struct link_map *map, Lmid_t lmid, uintptr_t *cookie)
+{
+  /* The linux-gate.so is placed at a fixed address, thus l_addr being 0,
+     and it might be the value reported as the AT_SYSINFO_EHDR.  */
+  if (map->l_addr == 0 && startswith (map->l_name, "linux-gate.so"))
+    fprintf (stderr, "vdso found: %p\n", NULL);
+  else if (map->l_addr == getauxval (AT_SYSINFO_EHDR))
+    fprintf (stderr, "vdso found: %p\n", (void*) map->l_addr);
+
+  return 0;
+}

include/dlfcn.h

@@ -12,6 +12,8 @@
 #define __RTLD_AUDIT	0x08000000
 #define __RTLD_SECURE	0x04000000 /* Apply additional security checks.  */
 #define __RTLD_NOIFUNC	0x02000000 /* Suppress calling ifunc functions.  */
+#define __RTLD_VDSO	0x01000000 /* Tell _dl_new_object the object is
+				      system-loaded.  */
 
 #define __LM_ID_CALLER	-2