libvtv/vtv_malloc.cc

   1 /* Copyright (C) 2012-2024 Free Software Foundation, Inc.
   2
   3    This file is part of GCC.
   4
   5    GCC is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3, or (at your option)
   8    any later version.
   9
  10    GCC is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    Under Section 7 of GPL version 3, you are granted additional
  16    permissions described in the GCC Runtime Library Exception, version
  17    3.1, as published by the Free Software Foundation.
  18
  19    You should have received a copy of the GNU General Public License and
  20    a copy of the GCC Runtime Library Exception along with this program;
  21    see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  22    <http://www.gnu.org/licenses/>.  */
  23
  24 /* This file is part of the vtable verification runtime library.  It
  25    contains our memory allocation and deallocation routines, which we
  26    use in order to keep track of the pages in memory in which our sets
  27    of valid vtable pointes are stored.  (We need to know the pages so
  28    we can set the protections on them appropriately).  For more
  29    information about the vtable verification feature, see the comments
  30    in vtv_rts.cc.  We use the existing obstack implementation in our
  31    memory allocation scheme.  */
  32
  33 #include <stdlib.h>
  34 #include <unistd.h>
  35 #if defined (__CYGWIN__) || defined (__MINGW32__)
  36 #define WIN32_LEAN_AND_MEAN
  37 #include <windows.h>
  38 #else
  39 #include <sys/mman.h>
  40 #endif
  41 #include <sys/types.h>
  42 #include <sys/stat.h>
  43 #include <fcntl.h>
  44 #include <stdio.h>
  45
  46 #include "vtv_utils.h"
  47 #include "vtv_malloc.h"
  48 #include "obstack.h"
  49
  50 /* The following variables are used only for debugging and performance tuning
  51    purposes. Therefore they do not need to be "protected".  They cannot be used
  52    to attack the vtable verification system and if they become corrupted it will
  53    not affect the correctness or security of any of the rest of the vtable
  54    verification feature.  */
  55
  56 unsigned int num_calls_to_mprotect = 0;
  57 unsigned int num_pages_protected = 0;
  58 unsigned int long long mprotect_cycles = 0;
  59
  60 /* Put the following variables in our ".vtable_map_vars" section so
  61    that they are protected.  They are explicitly unprotected and
  62    protected again by calls to __vtv_unprotect and __vtv_protect */
  63
  64 static struct obstack vtv_obstack VTV_PROTECTED_VAR;
  65 static void *current_chunk VTV_PROTECTED_VAR = 0;
  66 static size_t current_chunk_size VTV_PROTECTED_VAR = 0;
  67 static int malloc_initialized VTV_PROTECTED_VAR = 0;
  68
  69 #if defined (__CYGWIN__) || defined (__MINGW32__)
  70 //sysconf(_SC_PAGE_SIZE) port
  71 long sysconf_SC_PAGE_SIZE()
  72 {
  73   SYSTEM_INFO si;
  74   GetSystemInfo(&si);
  75   long pageSize = (long)si.dwPageSize;
  76   return pageSize;
  77   //return 4096; // standard usermode 32bit pagesize in bytes // FIXME
  78 }
  79 #endif
  80
  81 /* The function goes through and counts all the pages we have allocated
  82    so far.  It returns the page count.  */
  83
  84 int
  85 __vtv_count_mmapped_pages (void)
  86 {
  87   int count = 0;
  88   struct _obstack_chunk * ci = (struct _obstack_chunk *) current_chunk;
  89   while (ci)
  90     {
  91       count++;
  92       ci = ci->prev;
  93     }
  94
  95   return count;
  96 }
  97
  98 /* This function goes through all of the pages we have allocated so
  99    far and calls mprotect to change the protections on the pages,
 100    according to the value of PROTECTION_FLAG.  */
 101
 102 static void
 103 change_protections_on_data_chunks (int protection_flag)
 104 {
 105   struct _obstack_chunk *ci;
 106   ci = (struct _obstack_chunk *) current_chunk;
 107
 108   while (ci)
 109     {
 110       /* Initial set up for mprotect call.*/
 111       struct _obstack_chunk *protect_start = ci;
 112       size_t chunk_size;
 113       size_t total_size;
 114       unsigned int num_pages_in_chunk;
 115       char *next_page;
 116       unsigned long long start, end;
 117       int result;
 118
 119
 120       /* As long as the next 'chunk' is adjacent to the current one,
 121          keep going down the list.  */
 122       do
 123         {
 124           chunk_size = (ci->limit - (char *) ci);
 125           total_size = (ci->limit - (char *) protect_start);
 126           num_pages_in_chunk = chunk_size / VTV_PAGE_SIZE;
 127           if (chunk_size % VTV_PAGE_SIZE > 0)
 128             num_pages_in_chunk++;
 129           next_page = (char *) ci + (num_pages_in_chunk * VTV_PAGE_SIZE);
 130           ci = ci->prev;
 131         } while (ci && (char *) ci == next_page);
 132
 133       VTV_DEBUG_ASSERT (((unsigned long) protect_start & (VTV_PAGE_SIZE - 1))
 134                                                                        == 0);
 135
 136       /* Protect the contiguous chunks so far.  */
 137       start = rdtsc ();
 138       result = mprotect (protect_start, total_size, protection_flag);
 139       end = rdtsc ();
 140       mprotect_cycles += end - start;
 141       if (result == -1)
 142         VTV_error ();
 143       num_calls_to_mprotect++;
 144       num_pages_protected += (total_size + VTV_PAGE_SIZE - 1)/ VTV_PAGE_SIZE;
 145     }
 146
 147 #ifdef VTV_DEBUG
 148     __vtv_malloc_dump_stats ();
 149 #endif
 150 }
 151
 152 /* This function makes all of our allocated pages read-only.  */
 153
 154 void
 155 __vtv_malloc_protect (void)
 156 {
 157   change_protections_on_data_chunks (PROT_READ);
 158 }
 159
 160 /* This function makes all of our allocated pages read-write.  */
 161
 162 void
 163 __vtv_malloc_unprotect (void)
 164 {
 165   change_protections_on_data_chunks (PROT_READ | PROT_WRITE);
 166 }
 167
 168 /* Allocates a SIZE-sized chunk of memory that is aligned to a page
 169    boundary.  The amount of memory requested (SIZE) must be a multiple
 170    of the page size.  Note: We must use mmap to allocate the memory;
 171    using malloc here will cause problems.  */
 172
 173 static void *
 174 obstack_chunk_alloc (size_t size)
 175 {
 176   /* Increase size to the next multiple of VTV_PAGE_SIZE.   */
 177   size = (size + (VTV_PAGE_SIZE - 1)) & (~(VTV_PAGE_SIZE - 1));
 178   VTV_DEBUG_ASSERT ((size & (VTV_PAGE_SIZE - 1)) == 0);
 179   void *allocated;
 180
 181 #if defined (__CYGWIN__) || defined (__MINGW32__)
 182   if ((allocated = VirtualAlloc(NULL, size,  MEM_RESERVE|MEM_COMMIT,
 183                          PAGE_READWRITE)) == 0)
 184 #else
 185   if ((allocated = mmap (NULL, size, PROT_READ | PROT_WRITE,
 186                          MAP_PRIVATE | MAP_ANONYMOUS,  -1, 0)) == 0)
 187 #endif
 188     VTV_error ();
 189
 190   VTV_DEBUG_ASSERT (((unsigned long) allocated & (VTV_PAGE_SIZE - 1)) == 0);
 191
 192   current_chunk = allocated;
 193   current_chunk_size = size;
 194   return allocated;
 195 }
 196
 197 static void
 198 obstack_chunk_free (void *)
 199 {
 200   /* Do nothing. For our purposes there should be very little
 201      de-allocation. */
 202 }
 203
 204 /* This function sets up and initializes the obstack pieces for our
 205    memory allocation scheme.  */
 206
 207 void
 208 __vtv_malloc_init (void)
 209 {
 210   /* Make sure we only execute the main body of this function ONCE.  */
 211   if (malloc_initialized)
 212     return;
 213
 214 #if defined (__CYGWIN__) || defined (__MINGW32__)
 215   if (VTV_PAGE_SIZE != sysconf_SC_PAGE_SIZE())
 216 #else
 217   if (VTV_PAGE_SIZE != sysconf (_SC_PAGE_SIZE))
 218 #endif
 219     VTV_error ();
 220
 221   /* We guarantee that the obstack alloc failed handler will never be
 222      called because in case the allocation of the chunk fails, it will
 223      never return */
 224   obstack_alloc_failed_handler = NULL;
 225
 226   obstack_specify_allocation (&vtv_obstack, VTV_PAGE_SIZE, sizeof (long),
 227                               obstack_chunk_alloc, obstack_chunk_free);
 228   malloc_initialized = 1;
 229 }
 230
 231 /* This is our external interface for the memory allocation.  SIZE is
 232    the requested number of bytes to be allocated/  */
 233
 234 void *
 235 __vtv_malloc (size_t size)
 236 {
 237   return obstack_alloc (&vtv_obstack, size);
 238 }
 239
 240
 241 /* This is our external interface for memory deallocation.  */
 242
 243 void
 244 __vtv_free (void *)
 245 {
 246   /* Do nothing. We dont care about recovering unneded memory at this
 247      time.  */
 248 }
 249
 250
 251 /* This is a debugging function tat collects statistics about our
 252    memory allocation.  */
 253 void
 254 __vtv_malloc_stats (void)
 255 {
 256   int count = 0;
 257   struct _obstack_chunk * ci = (struct _obstack_chunk *) current_chunk;
 258   while (ci)
 259     {
 260       count++;
 261       ci = ci->prev;
 262     }
 263   fprintf (stderr,
 264            "__vtv_malloc_stats:\n  Page Size = %lu bytes\n  "
 265            "Number of pages = %d\n", static_cast<unsigned long>(VTV_PAGE_SIZE),
 266            count);
 267 }
 268
 269 /* This is a debugging function.  It writes out our memory allocation
 270    statistics to a log file.  */
 271
 272 void
 273 __vtv_malloc_dump_stats (void)
 274 {
 275   static int fd = -1;
 276
 277   if (fd == -1)
 278     fd = __vtv_open_log ("vtv_mem_protection.log");
 279   if (fd == -1)
 280     return;
 281
 282   int count = 0;
 283   struct _obstack_chunk * ci = (struct _obstack_chunk *) current_chunk;
 284   while (ci)
 285     {
 286       count++;
 287       ci = ci->prev;
 288     }
 289
 290   __vtv_add_to_log (fd, "__vtv_malloc_protect protected=%d pages\n", count);
 291 }