[glibc/azanella/ld-audit-fixes] elf: Fix initial-exec TLS access on audit modules (BZ #28096)

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c342a9f2ddeaf2e42eaede359c64bdb62481af6c

commit c342a9f2ddeaf2e42eaede359c64bdb62481af6c
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Thu Jul 15 09:02:36 2021 -0300

    elf: Fix initial-exec TLS access on audit modules (BZ #28096)
    
    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, i686-linux-gnu, and aarch64-linux-gnu.

Diff:
---
 elf/Makefile          |  8 ++++++
 elf/dl-object.c       |  3 ++
 elf/dl-tls.c          | 16 ++++++++---
 elf/rtld.c            |  2 ++
 elf/tst-audit21.c     | 42 +++++++++++++++++++++++++++
 elf/tst-auditmod21a.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++
 elf/tst-auditmod21b.c | 22 ++++++++++++++
 include/link.h        |  2 ++
 8 files changed, 171 insertions(+), 4 deletions(-)

diff --git a/elf/Makefile b/elf/Makefile
index 4636a2743a..587df12b3d 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -234,6 +234,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-audit19a \
 	 tst-audit19b \
 	 tst-audit20 \
+	 tst-audit21 \
 #	 reldep9
 tests-internal += loadtest unload unload2 circleload1 \
 	 neededtest neededtest2 neededtest3 neededtest4 \
@@ -380,6 +381,8 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
 		tst-auditmod19b \
 		tst-audit19bmod \
 		tst-auditmod20 \
+		tst-auditmod21a \
+		tst-auditmod21b \
 
 # Most modules build with _ISOMAC defined, but those filtered out
 # depend on internal headers.
@@ -1575,6 +1578,11 @@ 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
+
 # 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 9260d2d696..512ed9a9dc 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 73a852ad42..faba319e5c 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1055,6 +1055,8 @@ 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;
 }
 
 /* Load all audit modules.  */
diff --git a/elf/tst-audit21.c b/elf/tst-audit21.c
new file mode 100644
index 0000000000..307cb6fc3b
--- /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 *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;
+}
diff --git a/elf/tst-auditmod21a.c b/elf/tst-auditmod21a.c
new file mode 100644
index 0000000000..a0584f36e6
--- /dev/null
+++ b/elf/tst-auditmod21a.c
@@ -0,0 +1,80 @@
+/* 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;
+
+/* Defined tst-auditmod21b.so  */
+extern __thread int tls_var2;
+extern __thread int tls_var3;
+
+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;
+
+  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 ();
+}
diff --git a/elf/tst-auditmod21b.c b/elf/tst-auditmod21b.c
new file mode 100644
index 0000000000..550f858b1d
--- /dev/null
+++ b/elf/tst-auditmod21b.c
@@ -0,0 +1,22 @@
+/* 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/>.  */
+
+#define tls_ie __attribute__ ((tls_model ("initial-exec")))
+
+__thread int tls_var2 tls_ie;
+__thread int tls_var3 tls_ie = 0x20;
diff --git a/include/link.h b/include/link.h
index 6a9f788d2b..ba4c588873 100644
--- a/include/link.h
+++ b/include/link.h
@@ -195,6 +195,8 @@ 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.*/