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1  // Copyright (c) 2013 The Chromium Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style license that can be
3  // found in the LICENSE file.
4  
5  #include "crazy_linker_ashmem.h"
6  
7  #include <fcntl.h>
8  #include <string.h>
9  #include <sys/ioctl.h>
10  #include <sys/stat.h>
11  #include <sys/types.h>
12  #include <unistd.h>
13  
14  #include <linux/ashmem.h>
15  
16  #include "crazy_linker_system.h"
17  #include "crazy_linker_memory_mapping.h"
18  
19  namespace crazy {
20  
Allocate(size_t region_size,const char * region_name)21  bool AshmemRegion::Allocate(size_t region_size, const char* region_name) {
22    int fd = TEMP_FAILURE_RETRY(open("/dev/ashmem", O_RDWR));
23    if (fd < 0)
24      return false;
25  
26    if (ioctl(fd, ASHMEM_SET_SIZE, region_size) < 0)
27      goto ERROR;
28  
29    if (region_name) {
30      char buf[256];
31      strlcpy(buf, region_name, sizeof(buf));
32      if (ioctl(fd, ASHMEM_SET_NAME, buf) < 0)
33        goto ERROR;
34    }
35  
36    Reset(fd);
37    return true;
38  
39  ERROR:
40    ::close(fd);
41    return false;
42  }
43  
SetProtectionFlags(int prot)44  bool AshmemRegion::SetProtectionFlags(int prot) {
45    return ioctl(fd_, ASHMEM_SET_PROT_MASK, prot) == 0;
46  }
47  
48  // static
CheckFileDescriptorIsReadOnly(int fd)49  bool AshmemRegion::CheckFileDescriptorIsReadOnly(int fd) {
50    const size_t map_size = PAGE_SIZE;
51    ScopedMemoryMapping map;
52  
53    // First, check that trying to map a page of the region with PROT_WRITE
54    // fails with EPERM.
55    if (map.Allocate(NULL, map_size, MemoryMapping::CAN_WRITE, fd)) {
56      LOG("%s: Region could be mapped writable. Should not happen.\n",
57          __FUNCTION__);
58      errno = EPERM;
59      return false;
60    }
61    if (errno != EPERM) {
62      LOG_ERRNO("%s: Region failed writable mapping with unexpected error",
63                __FUNCTION__);
64      return false;
65    }
66  
67    // Second, check that it can be mapped PROT_READ, but cannot be remapped
68    // with PROT_READ | PROT_WRITE through mprotect().
69    if (!map.Allocate(NULL, map_size, MemoryMapping::CAN_READ, fd)) {
70      LOG_ERRNO("%s: Failed to map region read-only", __FUNCTION__);
71      return false;
72    }
73    if (map.SetProtection(MemoryMapping::CAN_READ_WRITE)) {
74      LOG_ERRNO("%s: Region could be remapped read-write. Should not happen.\n",
75                __FUNCTION__);
76      return false;
77    }
78    if (errno != EACCES) {
79      LOG_ERRNO(
80          "%s: Region failed to be remapped read-write with unexpected error",
81          __FUNCTION__);
82      return false;
83    }
84  
85    // Everything's good.
86    return true;
87  }
88  
89  }  // namespace crazy
90