elf: Fix initial-exec TLS access on audit modules (BZ #28096)

For audit modules and 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 audit setup.  However, subsequent thread
creation would need to follow the default behaviour.

This patch fixes it by setting l_auditing link_map field not only
for the audit modules, but also for all its dependencies.  This is
used on _dl_allocate_tls_init to avoid the static TLS initialization
at load time.

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

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>

elf/Makefile

@@ -377,6 +377,7 @@ tests += \
   tst-audit18 \
   tst-audit19b \
   tst-audit20 \
+  tst-audit21 \
   tst-audit22 \
   tst-audit23 \
   tst-auditmany \
@@ -697,6 +698,8 @@ modules-names = \
   tst-auditmod19a \
   tst-auditmod19b \
   tst-auditmod20 \
+  tst-auditmod21a \
+  tst-auditmod21b \
   tst-auditmod22 \
   tst-auditmod23 \
   tst-auxvalmod \
@@ -2139,6 +2142,11 @@ tst-audit19b-ARGS = -- $(host-test-program-cmd)
 $(objpfx)tst-audit20.out: $(objpfx)tst-auditmod20.so
 tst-audit20-ENV = LD_AUDIT=$(objpfx)tst-auditmod20.so
 
+$(objpfx)tst-audit21: $(shared-thread-library)
+$(objpfx)tst-audit21.out: $(objpfx)tst-auditmod21a.so
+$(objpfx)tst-auditmod21a.so: $(objpfx)tst-auditmod21b.so
+tst-audit21-ENV = LD_AUDIT=$(objpfx)tst-auditmod21a.so
+
 $(objpfx)tst-audit22.out: $(objpfx)tst-auditmod22.so
 tst-audit22-ARGS = -- $(host-test-program-cmd)
 

elf/dl-tls.c

@@ -519,8 +519,12 @@ _dl_resize_dtv (dtv_t *dtv, size_t max_modid)
 }
 
 
+/* Allocate initial TLS.  RESULT should be a non-NULL pointer to storage
+   for the TLS space.  The DTV may be resized, and so this function may
+   call malloc to allocate that space.  The loader's GL(dl_load_tls_lock)
+   is taken when manipulating global TLS-related data in the loader.  */
 void *
-_dl_allocate_tls_init (void *result)
+_dl_allocate_tls_init (void *result, bool init_tls)
 {
   if (result == NULL)
     /* The memory allocation failed.  */
@@ -593,7 +597,14 @@ _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.  */
+	  /* Copy the initialization image and clear the BSS part.  For
+	     audit 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 audit setup.  However,
+	     subsequent thread creation would need to follow the default
+	     behaviour.   */
+	  if (map->l_ns != LM_ID_BASE && !init_tls)
+	    continue;
 	  memset (__mempcpy (dest, map->l_tls_initimage,
 			     map->l_tls_initimage_size), '\0',
 		  map->l_tls_blocksize - map->l_tls_initimage_size);
@@ -620,7 +631,7 @@ _dl_allocate_tls (void *mem)
 {
   return _dl_allocate_tls_init (mem == NULL
 				? _dl_allocate_tls_storage ()
-				: allocate_dtv (mem));
+				: allocate_dtv (mem), true);
 }
 rtld_hidden_def (_dl_allocate_tls)
 

elf/rtld.c

@@ -2462,7 +2462,7 @@ dl_main (const ElfW(Phdr) *phdr,
      into the main thread's TLS area, which we allocated above.
      Note: thread-local variables must only be accessed after completing
      the next step.  */
-  _dl_allocate_tls_init (tcbp);
+  _dl_allocate_tls_init (tcbp, false);
 
   /* And finally install it for the main thread.  */
   if (! tls_init_tp_called)

elf/tst-audit21.c

@@ -0,0 +1,42 @@
+/* Check LD_AUDIT with static TLS.
+   Copyright (C) 2022 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 *arg)
+{
+  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;
+}

elf/tst-auditmod21a.c

@@ -0,0 +1,80 @@
+/* Check LD_AUDIT with static TLS.
+   Copyright (C) 2022 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;
+
+/* Defined at tst-auditmod21b.so  */
+extern __thread int tls_var2;
+extern __thread int tls_var3;
+
+static volatile int out;
+
+static void
+call_libc (void)
+{
+  /* isspace accesses 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;
+
+  tls_var2 = 0x2;
+  if (tls_var3 != 0x20)
+    abort ();
+  tls_var3 = 0x40;
+
+  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 ();
+}

elf/tst-auditmod21b.c

@@ -0,0 +1,22 @@
+/* Check LD_AUDIT with static TLS.
+   Copyright (C) 2022 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/>.  */
+
+#define tls_ie __attribute__ ((tls_model ("initial-exec")))
+
+__thread int tls_var2 tls_ie;
+__thread int tls_var3 tls_ie = 0x20;

nptl/allocatestack.c

@@ -138,7 +138,7 @@ get_cached_stack (size_t *sizep, void **memp)
   memset (dtv, '\0', (dtv[-1].counter + 1) * sizeof (dtv_t));
 
   /* Re-initialize the TLS.  */
-  _dl_allocate_tls_init (TLS_TPADJ (result));
+  _dl_allocate_tls_init (TLS_TPADJ (result), true);
 
   return result;
 }

sysdeps/generic/ldsodefs.h

@@ -1282,7 +1282,7 @@ extern void _dl_allocate_static_tls (struct link_map *map) attribute_hidden;
 /* These are internal entry points to the two halves of _dl_allocate_tls,
    only used within rtld.c itself at startup time.  */
 extern void *_dl_allocate_tls_storage (void) attribute_hidden;
-extern void *_dl_allocate_tls_init (void *);
+extern void *_dl_allocate_tls_init (void *, bool);
 rtld_hidden_proto (_dl_allocate_tls_init)
 
 /* Deallocate memory allocated with _dl_allocate_tls.  */