Add framework for tunables

The tunables framework allows us to uniformly manage and expose global
variables inside glibc as switches to users.  tunables/README has
instructions for glibc developers to add new tunables.

Tunables support can be enabled by passing the --enable-tunables
configure flag to the configure script.  This patch only adds a
framework and does not pose any limitations on how tunable values are
read from the user.  It also adds environment variables used in malloc
behaviour tweaking to the tunables framework as a PoC of the
compatibility interface.

	* manual/install.texi: Add --enable-tunables option.
	* INSTALL: Regenerate.
	* README.tunables: New file.
	* Makeconfig (CPPFLAGS): Define TOP_NAMESPACE.
	(before-compile): Generate dl-tunable-list.h early.
	* config.h.in: Add HAVE_TUNABLES.
	* config.make.in: Add have-tunables.
	* configure.ac: Add --enable-tunables option.
	* configure: Regenerate.
	* csu/init-first.c (__libc_init_first): Move
	__libc_init_secure earlier...
	* csu/init-first.c (LIBC_START_MAIN):... to here.
	Include dl-tunables.h, libc-internal.h.
	(LIBC_START_MAIN) [!SHARED]: Initialize tunables for static
	binaries.
	* elf/Makefile (dl-routines): Add dl-tunables.
	* elf/Versions (ld): Add __tunable_set_val to GLIBC_PRIVATE
	namespace.
	* elf/dl-support (_dl_nondynamic_init): Unset MALLOC_CHECK_
	only when !HAVE_TUNABLES.
	* elf/rtld.c (process_envvars): Likewise.
	* elf/dl-sysdep.c [HAVE_TUNABLES]: Include dl-tunables.h
	(_dl_sysdep_start): Call __tunables_init.
	* elf/dl-tunable-types.h: New file.
	* elf/dl-tunables.c: New file.
	* elf/dl-tunables.h: New file.
	* elf/dl-tunables.list: New file.
	* malloc/tst-malloc-usable-static.c: New test case.
	* malloc/Makefile (tests-static): Add it.
	* malloc/arena.c [HAVE_TUNABLES]: Include dl-tunables.h.
	Define TUNABLE_NAMESPACE.
	(DL_TUNABLE_CALLBACK (set_mallopt_check)): New function.
	(DL_TUNABLE_CALLBACK_FNDECL): New macro.  Use it to define
	callback functions.
	(ptmalloc_init): Set tunable values.
	* scripts/gen-tunables.awk: New file.
	* sysdeps/mach/hurd/dl-sysdep.c: Include dl-tunables.h.
	(_dl_sysdep_start): Call __tunables_init.

1 files changed, 320 insertions, 0 deletions

diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
new file mode 100644
index 0000000..472747b
--- /dev/null
+++ b/elf/dl-tunables.c
@@ -0,0 +1,320 @@
+/* The tunable framework.  See the README.tunables to know how to use the
+   tunable in a glibc module.
+
+   Copyright (C) 2016 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <libc-internal.h>
+#include <sysdep.h>
+#include <fcntl.h>
+#include <ldsodefs.h>
+
+#define TUNABLES_INTERNAL 1
+#include "dl-tunables.h"
+
+/* Compare environment names, bounded by the name hardcoded in glibc.  */
+static bool
+is_name (const char *orig, const char *envname)
+{
+  for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
+    if (*orig != *envname)
+      break;
+
+  /* The ENVNAME is immediately followed by a value.  */
+  if (*orig == '\0' && *envname == '=')
+    return true;
+  else
+    return false;
+}
+
+static char **
+get_next_env (char **envp, char **name, size_t *namelen, char **val)
+{
+  while (envp != NULL && *envp != NULL)
+    {
+      char *envline = *envp;
+      int len = 0;
+
+      while (envline[len] != '\0' && envline[len] != '=')
+	len++;
+
+      /* Just the name and no value, go to the next one.  */
+      if (envline[len] == '\0')
+	continue;
+
+      *name = envline;
+      *namelen = len;
+      *val = &envline[len + 1];
+
+      return ++envp;
+    }
+
+  return NULL;
+}
+
+static int
+tunables_unsetenv (char **ep, const char *name)
+{
+  while (*ep != NULL)
+    {
+      size_t cnt = 0;
+
+      while ((*ep)[cnt] == name[cnt] && name[cnt] != '\0')
+	++cnt;
+
+      if (name[cnt] == '\0' && (*ep)[cnt] == '=')
+	{
+	  /* Found it.  Remove this pointer by moving later ones to
+	     the front.  */
+	  char **dp = ep;
+
+	  do
+	    dp[0] = dp[1];
+	  while (*dp++);
+	  /* Continue the loop in case NAME appears again.  */
+	}
+      else
+	++ep;
+    }
+
+  return 0;
+}
+
+/* A stripped down strtoul-like implementation for very early use.  It does not
+   set errno if the result is outside bounds because it gets called before
+   errno may have been set up.  */
+static unsigned long int
+tunables_strtoul (const char *nptr)
+{
+  unsigned long int result = 0;
+  long int sign = 1;
+  unsigned max_digit;
+
+  while (*nptr == ' ' || *nptr == '\t')
+    ++nptr;
+
+  if (*nptr == '-')
+    {
+      sign = -1;
+      ++nptr;
+    }
+  else if (*nptr == '+')
+    ++nptr;
+
+  if (*nptr < '0' || *nptr > '9')
+    return 0UL;
+
+  int base = 10;
+  max_digit = 9;
+  if (*nptr == '0')
+    {
+      if (nptr[1] == 'x' || nptr[1] == 'X')
+	{
+	  base = 16;
+	  nptr += 2;
+	}
+      else
+	{
+	  base = 8;
+	  max_digit = 7;
+	}
+    }
+
+  while (1)
+    {
+      unsigned long int digval;
+      if (*nptr >= '0' && *nptr <= '0' + max_digit)
+        digval = *nptr - '0';
+      else if (base == 16)
+        {
+	  if (*nptr >= 'a' && *nptr <= 'f')
+	    digval = *nptr - 'a' + 10;
+	  else if (*nptr >= 'A' && *nptr <= 'F')
+	    digval = *nptr - 'A' + 10;
+	  else
+	    break;
+	}
+      else
+        break;
+
+      if (result > ULONG_MAX / base
+	  || (result == ULONG_MAX / base && digval > ULONG_MAX % base))
+	return ULONG_MAX;
+      result *= base;
+      result += digval;
+      ++nptr;
+    }
+
+  return result * sign;
+}
+
+/* Initialize the internal type if the value validates either using the
+   explicit constraints of the tunable or with the implicit constraints of its
+   type.  */
+static void
+tunable_set_val_if_valid_range (tunable_t *cur, const char *strval,
+				int64_t default_min, int64_t default_max)
+{
+  int64_t val = tunables_strtoul (strval);
+
+  int64_t min = cur->type.min;
+  int64_t max = cur->type.max;
+
+  if (min == max)
+    {
+      min = default_min;
+      max = default_max;
+    }
+
+  if (val >= min && val <= max)
+    {
+      cur->val.numval = val;
+      cur->strval = strval;
+    }
+}
+
+/* Validate range of the input value and initialize the tunable CUR if it looks
+   good.  */
+static void
+tunable_initialize (tunable_t *cur, const char *strval)
+{
+  switch (cur->type.type_code)
+    {
+    case TUNABLE_TYPE_INT_32:
+	{
+	  tunable_set_val_if_valid_range (cur, strval, INT32_MIN, INT32_MAX);
+	  break;
+	}
+    case TUNABLE_TYPE_SIZE_T:
+	{
+	  tunable_set_val_if_valid_range (cur, strval, 0, SIZE_MAX);
+	  break;
+	}
+    case TUNABLE_TYPE_STRING:
+	{
+	  cur->val.strval = cur->strval = strval;
+	  break;
+	}
+    default:
+      __builtin_unreachable ();
+    }
+}
+
+/* Disable a tunable if it is set.  */
+static void
+disable_tunable (tunable_id_t id, char **envp)
+{
+  const char *env_alias = tunable_list[id].env_alias;
+
+  if (env_alias != NULL)
+    tunables_unsetenv (envp, tunable_list[id].env_alias);
+}
+
+/* Disable the glibc.malloc.check tunable in SETUID/SETGID programs unless
+   the system administrator overrides it by creating the /etc/suid-debug
+   file.  This is a special case where we want to conditionally enable/disable
+   a tunable even for setuid binaries.  We use the special version of access()
+   to avoid setting ERRNO, which is a TLS variable since TLS has not yet been
+   set up.  */
+static inline void
+__always_inline
+maybe_disable_malloc_check (void)
+{
+  if (__libc_enable_secure && __access_noerrno ("/etc/suid-debug", F_OK) != 0)
+    disable_tunable (TUNABLE_ENUM_NAME(glibc, malloc, check), __environ);
+}
+
+/* Initialize the tunables list from the environment.  For now we only use the
+   ENV_ALIAS to find values.  Later we will also use the tunable names to find
+   values.  */
+void
+__tunables_init (char **envp)
+{
+  char *envname = NULL;
+  char *envval = NULL;
+  size_t len = 0;
+
+  maybe_disable_malloc_check ();
+
+  while ((envp = get_next_env (envp, &envname, &len, &envval)) != NULL)
+    {
+      for (int i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
+	{
+	  tunable_t *cur = &tunable_list[i];
+
+	  /* Skip over tunables that have either been set already or should be
+	     skipped.  */
+	  if (cur->strval != NULL || cur->env_alias == NULL
+	      || (__libc_enable_secure && !cur->is_secure))
+	    continue;
+
+	  const char *name = cur->env_alias;
+
+	  /* We have a match.  Initialize and move on to the next line.  */
+	  if (is_name (name, envname))
+	    {
+	      tunable_initialize (cur, envval);
+	      break;
+	    }
+	}
+    }
+}
+
+/* Set the tunable value.  This is called by the module that the tunable exists
+   in. */
+void
+__tunable_set_val (tunable_id_t id, void *valp, tunable_callback_t callback)
+{
+  tunable_t *cur = &tunable_list[id];
+
+  /* Don't do anything if our tunable was not set during initialization or if
+     it failed validation.  */
+  if (cur->strval == NULL)
+    return;
+
+  if (valp == NULL)
+    goto cb;
+
+  switch (cur->type.type_code)
+    {
+    case TUNABLE_TYPE_INT_32:
+	{
+	  *((int32_t *) valp) = (int32_t) cur->val.numval;
+	  break;
+	}
+    case TUNABLE_TYPE_SIZE_T:
+	{
+	  *((size_t *) valp) = (size_t) cur->val.numval;
+	  break;
+	}
+    case TUNABLE_TYPE_STRING:
+	{
+	  *((const char **)valp) = cur->val.strval;
+	  break;
+	}
+    default:
+      __builtin_unreachable ();
+    }
+
+cb:
+  if (callback)
+    callback (&cur->val);
+}