rtld: Add glibc.rtld.enable_secure tunable.

diff --git a/NEWS b/NEWS
index 8c1c149f91..b04fb15064 100644
--- a/NEWS
+++ b/NEWS
@@ -43,6 +43,10 @@  Major new features:
   on thread stack created by pthread_create or memory allocated by
   malloc).
 
+* A new tunable, glibc.rtld.enable_secure, used to set __libc_enable_secure
+  to 1.  Setting the tunable to 0 does *NOT* set __libc_enable_secure to 0.
+  Once the tunable is encountered all following tunables are ignored.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * The ldconfig program now skips file names containing ';' or ending in
diff --git a/csu/libc-start.c b/csu/libc-start.c
index c3bb6d09bc..2f546a3677 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -266,6 +266,10 @@  LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
 
   __tunables_init (__environ);
 
+  int32_t tes = TUNABLE_GET_FULL (glibc, rtld, enable_secure, int32_t, NULL);
+  if (tes == 1)
+    __libc_enable_secure = 1;
+
   ARCH_INIT_CPU_FEATURES ();
 
   /* Do static pie self relocation after tunables and cpu features
diff --git a/elf/Makefile b/elf/Makefile
index afec7be084..6c38a72b0d 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -285,6 +285,7 @@  tests-static-internal := \
   tst-tls1-static \
   tst-tls1-static-non-pie \
   tst-tunables \
+  tst-tunables-enable_secure \
   # tests-static-internal
 
 CRT-tst-tls1-static-non-pie := $(csu-objpfx)crt1.o
@@ -2672,6 +2673,7 @@  $(objpfx)tst-glibc-hwcaps-mask.out: \
 $(objpfx)tst-glibc-hwcaps-cache.out: $(objpfx)tst-glibc-hwcaps
 
 tst-tunables-ARGS = -- $(host-test-program-cmd)
+tst-tunables-enable_secure-ARGS = -- $(host-test-program-cmd)
 
 $(objpfx)list-tunables.out: tst-rtld-list-tunables.sh $(objpfx)ld.so
 	$(SHELL) $< $(objpfx)ld.so '$(test-wrapper-env)' \
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 644d21d1b0..d6c55cfaf2 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -250,7 +250,13 @@  parse_tunables (char *valstring)
     }
 
   for (int i = 0; i < ntunables; i++)
-    tunable_initialize (tunables[i].t, tunables[i].value);
+    {
+      tunable_initialize (tunables[i].t, tunables[i].value);
+
+      /* Ignore all tunables after encountering "glibc.rtld.enable_secure" */
+      if (tunable_strcmp(tunables[i].t->name, "glibc.rtld.enable_secure") == 0)
+	break;
+    }
 }
 
 /* Initialize the tunables list from the environment.  For now we only use the
diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
index 0df4dde24e..2d4fc84d74 100644
--- a/elf/dl-tunables.h
+++ b/elf/dl-tunables.h
@@ -164,4 +164,15 @@  tunable_is_name (const char *orig, const char *envname)
     return false;
 }
 
+/* Compare two strings. */
+static __always_inline int
+tunable_strcmp (const char *left, const char *right)
+{
+  for (;*left != '\0' && *right != '\0'; right++, left++)
+    if (*left != *right)
+      break;
+
+  return *left - *right;
+}
+
 #endif
diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
index 1b23fc9473..cb1b35854e 100644
--- a/elf/dl-tunables.list
+++ b/elf/dl-tunables.list
@@ -136,6 +136,12 @@  glibc {
       minval: 0
       default: 512
     }
+    enable_secure {
+      type: INT_32
+      minval: 0
+      maxval: 1
+      default: 0
+    }
   }
 
   mem {
diff --git a/elf/tst-rtld-list-tunables.exp b/elf/tst-rtld-list-tunables.exp
index 2233ea9c7c..db0e1c86e9 100644
--- a/elf/tst-rtld-list-tunables.exp
+++ b/elf/tst-rtld-list-tunables.exp
@@ -12,5 +12,6 @@  glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.malloc.top_pad: 0x20000 (min: 0x0, max: 0x[f]+)
 glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0x[f]+)
 glibc.rtld.dynamic_sort: 2 (min: 1, max: 2)
+glibc.rtld.enable_secure: 0 (min: 0, max: 1)
 glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
 glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0x[f]+)
diff --git a/elf/tst-tunables-enable_secure.c b/elf/tst-tunables-enable_secure.c
new file mode 100644
index 0000000000..e749ec9f17
--- /dev/null
+++ b/elf/tst-tunables-enable_secure.c
@@ -0,0 +1,115 @@ 
+/* Check GLIBC_TUNABLES parsing for enable_secure.
+   Copyright (C) 2023 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 <array_length.h>
+#include <dl-tunables.h>
+#include <getopt.h>
+#include <intprops.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <sys/auxv.h>
+#include <unistd.h>
+
+static int restart;
+#define CMDLINE_OPTIONS \
+  { "restart", no_argument, &restart, 1 },
+
+static const struct test_t
+{
+  const char *env;
+  int32_t expected_malloc_check;
+  int32_t expected_enable_secure;
+} tests[] =
+{
+  /* Expected tunable format.  */
+  {
+    "glibc.malloc.check=2:glibc.rtld.enable_secure=1",
+    2,
+    1,
+  },
+  /* Tunables encountered after enable_secure should be ignored. */
+  {
+    "glibc.rtld.enable_secure=1:glibc.malloc.check=2",
+    0,
+    1,
+  },
+};
+
+static int
+handle_restart (int i)
+{
+  TEST_COMPARE (tests[i].expected_malloc_check,
+		TUNABLE_GET_FULL (glibc, malloc, check, int32_t, NULL));
+  TEST_COMPARE (tests[i].expected_enable_secure,
+		TUNABLE_GET_FULL (glibc, rtld, enable_secure, int32_t, NULL));
+  if (tests[i].expected_enable_secure == 1)
+    {
+      TEST_COMPARE (1, __libc_enable_secure);
+    }
+  return 0;
+}
+
+static int
+do_test (int argc, char *argv[])
+{
+  /* We must have either:
+     - One or four parameters left if called initially:
+       + path to ld.so         optional
+       + "--library-path"      optional
+       + the library path      optional
+       + the application name
+       + the test to check  */
+
+  TEST_VERIFY_EXIT (argc == 2 || argc == 5);
+
+  if (restart)
+    return handle_restart (atoi (argv[1]));
+
+  char nteststr[INT_BUFSIZE_BOUND (int)];
+
+  char *spargv[10];
+  {
+    int i = 0;
+    for (; i < argc - 1; i++)
+      spargv[i] = argv[i + 1];
+    spargv[i++] = (char *) "--direct";
+    spargv[i++] = (char *) "--restart";
+    spargv[i++] = nteststr;
+    spargv[i] = NULL;
+  }
+
+  for (int i = 0; i < array_length (tests); i++)
+    {
+      snprintf (nteststr, sizeof nteststr, "%d", i);
+
+      printf ("[%d] Spawned test for %s\n", i, tests[i].env);
+      setenv ("GLIBC_TUNABLES", tests[i].env, 1);
+      struct support_capture_subprocess result
+	= support_capture_subprogram (spargv[0], spargv);
+      support_capture_subprocess_check (&result, "tst-tunables-enable_secure",
+		                        0, sc_allow_stderr);
+      support_capture_subprocess_free (&result);
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION_ARGV do_test
+#include <support/test-driver.c>