src/lib/malloc/map_anon.h

   1 /* Copyright (c) 2003-2004, Roger Dingledine
   2  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   3  * Copyright (c) 2007-2021, The Tor Project, Inc. */
   4 /* See LICENSE for licensing information */
   5
   6 /**
   7  * \file map_anon.h
   8  * \brief Headers for map_anon.c
   9  **/
  10
  11 #ifndef TOR_MAP_ANON_H
  12 #define TOR_MAP_ANON_H
  13
  14 #include "lib/malloc/malloc.h"
  15 #include <stddef.h>
  16
  17 /**
  18  * When this flag is specified, try to prevent the mapping from being
  19  * swapped or dumped.
  20  *
  21  * In some operating systems, this flag is not implemented.
  22  */
  23 #define ANONMAP_PRIVATE   (1u<<0)
  24 /**
  25  * When this flag is specified, try to prevent the mapping from being
  26  * inherited after a fork().  In some operating systems, trying to access it
  27  * afterwards will cause its contents to be zero.  In others, trying to access
  28  * it afterwards will cause a crash.
  29  *
  30  * In some operating systems, this flag is not implemented at all.
  31  */
  32 #define ANONMAP_NOINHERIT (1u<<1)
  33
  34 typedef enum {
  35   /** Possible value for inherit_result_out: the memory will be kept
  36    * by any child process. */
  37   INHERIT_RES_KEEP=0,
  38   /** Possible value for inherit_result_out: the memory will be dropped in the
  39    * child process. Attempting to access it will likely cause a segfault. */
  40   INHERIT_RES_DROP,
  41   /** Possible value for inherit_result_out: the memory will be cleared in
  42    * the child process. */
  43   INHERIT_RES_ZERO
  44 } inherit_res_t;
  45
  46 /* Here we define the NOINHERIT_CAN_FAIL macro if and only if
  47  * it's possible that ANONMAP_NOINHERIT might yield inheritable memory.
  48  */
  49 #ifdef _WIN32
  50 /* Windows can't fork, so NOINHERIT is never needed. */
  51 #elif defined(HAVE_MINHERIT)
  52 /* minherit() will always have a working MAP_INHERIT_NONE or MAP_INHERIT_ZERO.
  53  * NOINHERIT should always work.
  54  */
  55 #elif defined(HAVE_MADVISE)
  56 /* madvise() sometimes has neither MADV_DONTFORK and MADV_WIPEONFORK.
  57  * We need to be ready for the possibility it failed.
  58  *
  59  * (Linux added DONTFORK in 2.6.16 and WIPEONFORK in 4.14. If we someday
  60  * require 2.6.16 or later, we can assume that DONTFORK will work.)
  61  */
  62 #define NOINHERIT_CAN_FAIL
  63 #else
  64 #define NOINHERIT_CAN_FAIL
  65 #endif /* defined(_WIN32) || ... */
  66
  67 void *tor_mmap_anonymous(size_t sz, unsigned flags,
  68                          inherit_res_t *inherit_result_out);
  69 void tor_munmap_anonymous(void *mapping, size_t sz);
  70
  71 #endif /* !defined(TOR_MAP_ANON_H) */