Always enable pointer guard [BZ #18928]

Honoring the LD_POINTER_GUARD environment variable in AT_SECURE mode
has security implications.  This commit enables pointer guard
unconditionally, and the environment variable is now ignored.

        [BZ #18928]
        * sysdeps/generic/ldsodefs.h (struct rtld_global_ro): Remove
        _dl_pointer_guard member.
        * elf/rtld.c (_rtld_global_ro): Remove _dl_pointer_guard
        initializer.
        (security_init): Always set up pointer guard.
        (process_envvars): Do not process LD_POINTER_GUARD.

4 files changed, 22 insertions, 19 deletions

diff --git a/ChangeLog b/ChangeLog
index 997ad1381f..fa58b3042d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2015-10-15  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #18928]
+	* sysdeps/generic/ldsodefs.h (struct rtld_global_ro): Remove
+	_dl_pointer_guard member.
+	* elf/rtld.c (_rtld_global_ro): Remove _dl_pointer_guard
+	initializer.
+	(security_init): Always set up pointer guard.
+	(process_envvars): Do not process LD_POINTER_GUARD.
+
 2015-10-14  Joseph Myers  <joseph@codesourcery.com>
 
 	[BZ #19134]
diff --git a/NEWS b/NEWS
index d4e8b4adf2..0491a27a1e 100644
--- a/NEWS
+++ b/NEWS
@@ -16,11 +16,14 @@ Version 2.23
   18265, 18370, 18421, 18480, 18525, 18595, 18589, 18610, 18618, 18647,
   18661, 18674, 18675, 18681, 18724, 18757, 18778, 18781, 18787, 18789,
   18790, 18795, 18796, 18803, 18820, 18823, 18824, 18825, 18857, 18863,
-  18870, 18872, 18873, 18875, 18887, 18921, 18951, 18952, 18956, 18961,
-  18966, 18967, 18969, 18970, 18977, 18980, 18981, 18985, 19003, 19007,
-  19012, 19016, 19018, 19032, 19046, 19049, 19050, 19059, 19071, 19074,
-  19076, 19077, 19078, 19079, 19085, 19086, 19088, 19094, 19095, 19124,
-  19125, 19129, 19134
+  18870, 18872, 18873, 18875, 18887, 18921, 18928, 18951, 18952, 18956,
+  18961, 18966, 18967, 18969, 18970, 18977, 18980, 18981, 18985, 19003,
+  19007, 19012, 19016, 19018, 19032, 19046, 19049, 19050, 19059, 19071,
+  19074, 19076, 19077, 19078, 19079, 19085, 19086, 19088, 19094, 19095,
+  19124, 19125, 19129, 19134
+
+* The LD_POINTER_GUARD environment variable can no longer be used to
+  disable the pointer guard feature.  It is always enabled.
 
 * The obsolete header <regexp.h> has been removed.  Programs that require
   this header must be updated to use <regex.h> instead.
diff --git a/elf/rtld.c b/elf/rtld.c
index 1474c72cde..52160dfde6 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -162,7 +162,6 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_hwcap_mask = HWCAP_IMPORTANT,
     ._dl_lazy = 1,
     ._dl_fpu_control = _FPU_DEFAULT,
-    ._dl_pointer_guard = 1,
     ._dl_pagesize = EXEC_PAGESIZE,
     ._dl_inhibit_cache = 0,
 
@@ -709,15 +708,12 @@ security_init (void)
 #endif
 
   /* Set up the pointer guard as well, if necessary.  */
-  if (GLRO(dl_pointer_guard))
-    {
-      uintptr_t pointer_chk_guard = _dl_setup_pointer_guard (_dl_random,
-							     stack_chk_guard);
+  uintptr_t pointer_chk_guard
+    = _dl_setup_pointer_guard (_dl_random, stack_chk_guard);
 #ifdef THREAD_SET_POINTER_GUARD
-      THREAD_SET_POINTER_GUARD (pointer_chk_guard);
+  THREAD_SET_POINTER_GUARD (pointer_chk_guard);
 #endif
-      __pointer_chk_guard_local = pointer_chk_guard;
-    }
+  __pointer_chk_guard_local = pointer_chk_guard;
 
   /* We do not need the _dl_random value anymore.  The less
      information we leave behind, the better, so clear the
@@ -2471,9 +2467,6 @@ process_envvars (enum mode *modep)
 	      GLRO(dl_use_load_bias) = envline[14] == '1' ? -1 : 0;
 	      break;
 	    }
-
-	  if (memcmp (envline, "POINTER_GUARD", 13) == 0)
-	    GLRO(dl_pointer_guard) = envline[14] != '0';
 	  break;
 
 	case 14:
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 7f7ff72f88..0625826c3b 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -592,9 +592,6 @@ struct rtld_global_ro
   /* List of auditing interfaces.  */
   struct audit_ifaces *_dl_audit;
   unsigned int _dl_naudit;
-
-  /* 0 if internal pointer values should not be guarded, 1 if they should.  */
-  EXTERN int _dl_pointer_guard;
 };
 # define __rtld_global_attribute__
 # if IS_IN (rtld)