[PATCH v2 6/6] elf: Fix initial-exec TLS access on audit modules (BZ #28096)

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

For ldaudit modules or dependencies with initial-exec TLS, we can not
set the initial TLS image on default loader initialization because it
would already be set by the ldaudit setup.  However, subsequent thread
creation would need to follow the default behaviour.

This patch fixes by making_dl_new_object() sets a new link_map flag
'l_dont_set_tls_static' only for __RTLD_AUDIT modules.  The flag is
later reset on _dl_allocate_tls_init().

Checked on x86_64-linux-gnu.
---
 elf/Makefile         |  6 +++-
 elf/dl-object.c      |  3 ++
 elf/dl-tls.c         | 16 +++++++---
 elf/rtld.c           |  2 ++
 elf/tst-audit21.c    | 42 +++++++++++++++++++++++++++
 elf/tst-auditmod21.c | 69 ++++++++++++++++++++++++++++++++++++++++++++
 include/link.h       |  2 ++
 7 files changed, 135 insertions(+), 5 deletions(-)
 create mode 100644 elf/tst-audit21.c
 create mode 100644 elf/tst-auditmod21.c

diff --git a/elf/Makefile b/elf/Makefile
index c429023b66..498c4dc3b9 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -220,7 +220,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-dlopenfail-2 \
 	 tst-filterobj tst-filterobj-dlopen tst-auxobj tst-auxobj-dlopen \
 	 tst-audit14 tst-audit15 tst-audit16 tst-audit17 tst-audit18 \
-	 tst-audit19 tst-audit20 \
+	 tst-audit19 tst-audit20 tst-audit21 \
 	 tst-single_threaded tst-single_threaded-pthread \
 	 tst-tls-ie tst-tls-ie-dlmopen argv0test \
 	 tst-glibc-hwcaps tst-glibc-hwcaps-prepend tst-glibc-hwcaps-mask \
@@ -304,6 +304,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		tst-auditmod9a tst-auditmod9b \
 		tst-auditmod18 tst-auditmod19 \
 		tst-auditmod20 tst-audit20mod \
+		tst-auditmod21 \
 		$(if $(CXX),tst-unique3lib tst-unique3lib2 tst-unique4lib \
 		  tst-nodelete-uniquemod tst-nodelete-rtldmod \
 		  tst-nodelete-zmod \
@@ -1516,6 +1517,9 @@ $(objpfx)tst-audit20.out: $(objpfx)tst-auditmod20.so \
 			  $(objpfx)tst-audit20mod.so
 tst-audit20-ARGS = -- $(host-test-program-cmd)
 
+$(objpfx)tst-audit21.out: $(objpfx)tst-auditmod21.so
+tst-audit21-ENV = LD_AUDIT=$(objpfx)tst-auditmod21.so
+
 # tst-sonamemove links against an older implementation of the library.
 LDFLAGS-tst-sonamemove-linkmod1.so = \
   -Wl,--version-script=tst-sonamemove-linkmod1.map \
diff --git a/elf/dl-object.c b/elf/dl-object.c
index 1875599eb2..eb2158a84b 100644
--- a/elf/dl-object.c
+++ b/elf/dl-object.c
@@ -175,6 +175,9 @@ _dl_new_object (char *realname, const char *libname, int type,
 
   new->l_local_scope[0] = &new->l_searchlist;
 
+  if (mode & __RTLD_AUDIT)
+    new->l_dont_set_tls_static = 1;
+
   /* Determine the origin.  If allocating the link map for the main
      executable, the realname is not known and "".  In this case, the
      origin needs to be determined by other means.  However, in case
diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index 423e380f7c..4763fdb856 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -593,10 +593,18 @@ _dl_allocate_tls_init (void *result)
 	     some platforms use in static programs requires it.  */
 	  dtv[map->l_tls_modid].pointer.val = dest;
 
-	  /* Copy the initialization image and clear the BSS part.  */
-	  memset (__mempcpy (dest, map->l_tls_initimage,
-			     map->l_tls_initimage_size), '\0',
-		  map->l_tls_blocksize - map->l_tls_initimage_size);
+	  /* Copy the initialization image and clear the BSS part.  For
+	     ldaudit modules or depedencies with initial-exec TLS, we can not
+	     set the initial TLS image on default loader initialization
+	     because it would already be set by the ldaudit setup.  However,
+	     subsequent thread creation would need to follow the default
+	     behaviour.   */
+	  if (__glibc_unlikely (!map->l_dont_set_tls_static))
+	    memset (__mempcpy (dest, map->l_tls_initimage,
+			       map->l_tls_initimage_size), '\0',
+		    map->l_tls_blocksize - map->l_tls_initimage_size);
+	  else
+	    map->l_dont_set_tls_static = 0;
 	}
 
       total += cnt;
diff --git a/elf/rtld.c b/elf/rtld.c
index 374bf86a69..1312378b5f 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1053,6 +1053,8 @@ ERROR: audit interface '%s' requires version %d (maximum supported version %d);
 
   /* Mark the DSO as being used for auditing.  */
   dlmargs.map->l_auditing = 1;
+  /* Mark the DSO to not clear the TLS bss in tls initialization.  */
+  dlmargs.map->l_dont_set_tls_static = 1;
 }
 
 /* Notify the the audit modules that the object MAP has already been
diff --git a/elf/tst-audit21.c b/elf/tst-audit21.c
new file mode 100644
index 0000000000..7f4996d66f
--- /dev/null
+++ b/elf/tst-audit21.c
@@ -0,0 +1,42 @@
+/* Check DT_AUDIT with static TLS.
+   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 <ctype.h>
+#include <support/xthread.h>
+#include <support/check.h>
+
+static volatile __thread int out __attribute__ ((tls_model ("initial-exec")));
+
+static void *
+tf (void *)
+{
+  TEST_COMPARE (out, 0);
+  out = isspace (' ');
+  return NULL;
+}
+
+int main (int argc, char *argv[])
+{
+  TEST_COMPARE (out, 0);
+  out = isspace (' ');
+
+  pthread_t t = xpthread_create (NULL, tf, NULL);
+  xpthread_join (t);
+
+  return 0;
+}
diff --git a/elf/tst-auditmod21.c b/elf/tst-auditmod21.c
new file mode 100644
index 0000000000..e6248622f4
--- /dev/null
+++ b/elf/tst-auditmod21.c
@@ -0,0 +1,69 @@
+/* Check DT_AUDIT with static TLS.
+   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 <ctype.h>
+#include <stdlib.h>
+#include <link.h>
+
+#define tls_ie __attribute__ ((tls_model ("initial-exec")))
+
+__thread int tls_var0 tls_ie;
+__thread int tls_var1 tls_ie = 0x10;
+
+static volatile int out;
+
+static void
+call_libc (void)
+{
+  /* isspace() access the initial-exec glibc TLS variables, which are
+     setup in glibc initialization.  */
+  out = isspace (' ');
+}
+
+unsigned int
+la_version (unsigned int v)
+{
+  tls_var0 = 0x1;
+  if (tls_var1 != 0x10)
+    abort ();
+  tls_var1 = 0x20;
+  call_libc ();
+  return LAV_CURRENT;
+}
+
+unsigned int
+la_objopen (struct link_map* map, Lmid_t lmid, uintptr_t* cookie)
+{
+  call_libc ();
+  *cookie = (uintptr_t) map;
+  return 0;
+}
+
+void
+la_activity (uintptr_t* cookie, unsigned int flag)
+{
+  if (tls_var0 != 0x1 || tls_var1 != 0x20)
+    abort ();
+  call_libc ();
+}
+
+void
+la_preinit (uintptr_t* cookie)
+{
+  call_libc ();
+}
diff --git a/include/link.h b/include/link.h
index ebd0f511e2..aca6fa58dc 100644
--- a/include/link.h
+++ b/include/link.h
@@ -190,6 +190,8 @@ struct link_map
     unsigned int l_need_tls_init:1; /* Nonzero if GL(dl_init_static_tls)
 				       should be called on this link map
 				       when relocation finishes.  */
+    unsigned int l_dont_set_tls_static:1; /* Non zero if static TLS setup should
+					     not be initialized.  */
     unsigned int l_auditing:1;	/* Nonzero if the DSO is used in auditing.  */
     unsigned int l_audit_any_plt:1; /* Nonzero if at least one audit module
 				       is interested in the PLT interception.*/
-- 
2.30.2