1 /* Copyright (C) 2012-2021 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 #include <windows.h>
37 #else
38 #include <sys/mman.h>
39 #endif
40 #include <sys/types.h>
41 #include <sys/stat.h>
42 #include <fcntl.h>
43 #include <stdio.h>
44
45 #include "vtv_utils.h"
46 #include "vtv_malloc.h"
47 #include "obstack.h"
48
49 /* The following variables are used only for debugging and performance tuning
50 purposes. Therefore they do not need to be "protected". They cannot be used
51 to attack the vtable verification system and if they become corrupted it will
52 not affect the correctness or security of any of the rest of the vtable
53 verification feature. */
54
55 unsigned int num_calls_to_mprotect = 0;
56 unsigned int num_pages_protected = 0;
57 unsigned int long long mprotect_cycles = 0;
58
59 /* Put the following variables in our ".vtable_map_vars" section so
60 that they are protected. They are explicitly unprotected and
61 protected again by calls to __vtv_unprotect and __vtv_protect */
62
63 static struct obstack vtv_obstack VTV_PROTECTED_VAR;
64 static void *current_chunk VTV_PROTECTED_VAR = 0;
65 static size_t current_chunk_size VTV_PROTECTED_VAR = 0;
66 static int malloc_initialized VTV_PROTECTED_VAR = 0;
67
68 #if defined (__CYGWIN__) || defined (__MINGW32__)
69 //sysconf(_SC_PAGE_SIZE) port
sysconf_SC_PAGE_SIZE()70 long sysconf_SC_PAGE_SIZE()
71 {
72 SYSTEM_INFO si;
73 GetSystemInfo(&si);
74 long pageSize = (long)si.dwPageSize;
75 return pageSize;
76 //return 4096; // standard usermode 32bit pagesize in bytes // FIXME
77 }
78 #endif
79
80 /* The function goes through and counts all the pages we have allocated
81 so far. It returns the page count. */
82
83 int
__vtv_count_mmapped_pages(void)84 __vtv_count_mmapped_pages (void)
85 {
86 int count = 0;
87 struct _obstack_chunk * ci = (struct _obstack_chunk *) current_chunk;
88 while (ci)
89 {
90 count++;
91 ci = ci->prev;
92 }
93
94 return count;
95 }
96
97 /* This function goes through all of the pages we have allocated so
98 far and calls mprotect to change the protections on the pages,
99 according to the value of PROTECTION_FLAG. */
100
101 static void
change_protections_on_data_chunks(int protection_flag)102 change_protections_on_data_chunks (int protection_flag)
103 {
104 struct _obstack_chunk *ci;
105 ci = (struct _obstack_chunk *) current_chunk;
106
107 while (ci)
108 {
109 /* Initial set up for mprotect call.*/
110 struct _obstack_chunk *protect_start = ci;
111 size_t chunk_size;
112 size_t total_size;
113 unsigned int num_pages_in_chunk;
114 char *next_page;
115 unsigned long long start, end;
116 int result;
117
118
119 /* As long as the next 'chunk' is adjacent to the current one,
120 keep going down the list. */
121 do
122 {
123 chunk_size = (ci->limit - (char *) ci);
124 total_size = (ci->limit - (char *) protect_start);
125 num_pages_in_chunk = chunk_size / VTV_PAGE_SIZE;
126 if (chunk_size % VTV_PAGE_SIZE > 0)
127 num_pages_in_chunk++;
128 next_page = (char *) ci + (num_pages_in_chunk * VTV_PAGE_SIZE);
129 ci = ci->prev;
130 } while (ci && (char *) ci == next_page);
131
132 VTV_DEBUG_ASSERT (((unsigned long) protect_start & (VTV_PAGE_SIZE - 1))
133 == 0);
134
135 /* Protect the contiguous chunks so far. */
136 start = rdtsc ();
137 result = mprotect (protect_start, total_size, protection_flag);
138 end = rdtsc ();
139 mprotect_cycles += end - start;
140 if (result == -1)
141 VTV_error ();
142 num_calls_to_mprotect++;
143 num_pages_protected += (total_size + VTV_PAGE_SIZE - 1)/ VTV_PAGE_SIZE;
144 }
145
146 #ifdef VTV_DEBUG
147 __vtv_malloc_dump_stats ();
148 #endif
149 }
150
151 /* This function makes all of our allocated pages read-only. */
152
153 void
__vtv_malloc_protect(void)154 __vtv_malloc_protect (void)
155 {
156 change_protections_on_data_chunks (PROT_READ);
157 }
158
159 /* This function makes all of our allocated pages read-write. */
160
161 void
__vtv_malloc_unprotect(void)162 __vtv_malloc_unprotect (void)
163 {
164 change_protections_on_data_chunks (PROT_READ | PROT_WRITE);
165 }
166
167 /* Allocates a SIZE-sized chunk of memory that is aligned to a page
168 boundary. The amount of memory requested (SIZE) must be a multiple
169 of the page size. Note: We must use mmap to allocate the memory;
170 using malloc here will cause problems. */
171
172 static void *
obstack_chunk_alloc(size_t size)173 obstack_chunk_alloc (size_t size)
174 {
175 /* Increase size to the next multiple of VTV_PAGE_SIZE. */
176 size = (size + (VTV_PAGE_SIZE - 1)) & (~(VTV_PAGE_SIZE - 1));
177 VTV_DEBUG_ASSERT ((size & (VTV_PAGE_SIZE - 1)) == 0);
178 void *allocated;
179
180 #if defined (__CYGWIN__) || defined (__MINGW32__)
181 if ((allocated = VirtualAlloc(NULL, size, MEM_RESERVE|MEM_COMMIT,
182 PAGE_READWRITE)) == 0)
183 #else
184 if ((allocated = mmap (NULL, size, PROT_READ | PROT_WRITE,
185 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)) == 0)
186 #endif
187 VTV_error ();
188
189 VTV_DEBUG_ASSERT (((unsigned long) allocated & (VTV_PAGE_SIZE - 1)) == 0);
190
191 current_chunk = allocated;
192 current_chunk_size = size;
193 return allocated;
194 }
195
196 static void
obstack_chunk_free(void *)197 obstack_chunk_free (void *)
198 {
199 /* Do nothing. For our purposes there should be very little
200 de-allocation. */
201 }
202
203 /* This function sets up and initializes the obstack pieces for our
204 memory allocation scheme. */
205
206 void
__vtv_malloc_init(void)207 __vtv_malloc_init (void)
208 {
209 /* Make sure we only execute the main body of this function ONCE. */
210 if (malloc_initialized)
211 return;
212
213 #if defined (__CYGWIN__) || defined (__MINGW32__)
214 if (VTV_PAGE_SIZE != sysconf_SC_PAGE_SIZE())
215 #else
216 if (VTV_PAGE_SIZE != sysconf (_SC_PAGE_SIZE))
217 #endif
218 VTV_error ();
219
220 /* We guarantee that the obstack alloc failed handler will never be
221 called because in case the allocation of the chunk fails, it will
222 never return */
223 obstack_alloc_failed_handler = NULL;
224
225 obstack_specify_allocation (&vtv_obstack, VTV_PAGE_SIZE, sizeof (long),
226 obstack_chunk_alloc, obstack_chunk_free);
227 malloc_initialized = 1;
228 }
229
230 /* This is our external interface for the memory allocation. SIZE is
231 the requested number of bytes to be allocated/ */
232
233 void *
__vtv_malloc(size_t size)234 __vtv_malloc (size_t size)
235 {
236 return obstack_alloc (&vtv_obstack, size);
237 }
238
239
240 /* This is our external interface for memory deallocation. */
241
242 void
__vtv_free(void *)243 __vtv_free (void *)
244 {
245 /* Do nothing. We dont care about recovering unneded memory at this
246 time. */
247 }
248
249
250 /* This is a debugging function tat collects statistics about our
251 memory allocation. */
252 void
__vtv_malloc_stats(void)253 __vtv_malloc_stats (void)
254 {
255 int count = 0;
256 struct _obstack_chunk * ci = (struct _obstack_chunk *) current_chunk;
257 while (ci)
258 {
259 count++;
260 ci = ci->prev;
261 }
262 fprintf (stderr,
263 "__vtv_malloc_stats:\n Page Size = %lu bytes\n "
264 "Number of pages = %d\n", static_cast<unsigned long>(VTV_PAGE_SIZE),
265 count);
266 }
267
268 /* This is a debugging function. It writes out our memory allocation
269 statistics to a log file. */
270
271 void
__vtv_malloc_dump_stats(void)272 __vtv_malloc_dump_stats (void)
273 {
274 static int fd = -1;
275
276 if (fd == -1)
277 fd = __vtv_open_log ("vtv_mem_protection.log");
278 if (fd == -1)
279 return;
280
281 int count = 0;
282 struct _obstack_chunk * ci = (struct _obstack_chunk *) current_chunk;
283 while (ci)
284 {
285 count++;
286 ci = ci->prev;
287 }
288
289 __vtv_add_to_log (fd, "__vtv_malloc_protect protected=%d pages\n", count);
290 }
291