1// Copyright 2014 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
19namespace crazy {
20
21bool 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
39ERROR:
40  ::close(fd);
41  return false;
42}
43
44bool AshmemRegion::SetProtectionFlags(int prot) {
45  return ioctl(fd_, ASHMEM_SET_PROT_MASK, prot) == 0;
46}
47
48// static
49bool 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