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