1 /*
2 * Copyright (C) 2018 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "memfd.h"
18
19 #include <errno.h>
20 #include <stdio.h>
21 #if !defined(_WIN32)
22 #include <fcntl.h>
23 #include <sys/syscall.h>
24 #include <sys/utsname.h>
25 #include <unistd.h>
26 #endif
27 #if defined(__BIONIC__)
28 #include <linux/memfd.h> // To access memfd flags.
29 #endif
30
31 #include <android-base/logging.h>
32 #include <android-base/unique_fd.h>
33
34 #include "macros.h"
35
36 namespace art {
37
38 #if defined(__NR_memfd_create)
39
memfd_create(const char * name,unsigned int flags)40 int memfd_create(const char* name, unsigned int flags) {
41 // Check kernel version supports memfd_create(). Some older kernels segfault executing
42 // memfd_create() rather than returning ENOSYS (b/116769556).
43 static constexpr int kRequiredMajor = 3;
44 static constexpr int kRequiredMinor = 17;
45 struct utsname uts;
46 int major, minor;
47 if (uname(&uts) != 0 ||
48 strcmp(uts.sysname, "Linux") != 0 ||
49 sscanf(uts.release, "%d.%d", &major, &minor) != 2 ||
50 (major < kRequiredMajor || (major == kRequiredMajor && minor < kRequiredMinor))) {
51 errno = ENOSYS;
52 return -1;
53 }
54
55 return syscall(__NR_memfd_create, name, flags);
56 }
57
58 #else // __NR_memfd_create
59
60 int memfd_create([[maybe_unused]] const char* name, [[maybe_unused]] unsigned int flags) {
61 errno = ENOSYS;
62 return -1;
63 }
64
65 #endif // __NR_memfd_create
66
67 // This is a wrapper that will attempt to simulate memfd_create if normal running fails.
memfd_create_compat(const char * name,unsigned int flags)68 int memfd_create_compat(const char* name, unsigned int flags) {
69 int res = memfd_create(name, flags);
70 if (res >= 0) {
71 return res;
72 }
73 #if !defined(_WIN32)
74 // Try to create an anonymous file with tmpfile that we can use instead.
75 if (flags == 0) {
76 FILE* file = tmpfile();
77 if (file != nullptr) {
78 // We want the normal 'dup' semantics since memfd_create without any flags isn't CLOEXEC.
79 // Unfortunately on some android targets we will compiler error if we use dup directly and so
80 // need to use fcntl.
81 int nfd = fcntl(fileno(file), F_DUPFD, /*lowest allowed fd*/ 0);
82 fclose(file);
83 return nfd;
84 }
85 }
86 #endif
87 return res;
88 }
89
90 #if defined(__BIONIC__)
91
IsSealFutureWriteSupportedInternal()92 static bool IsSealFutureWriteSupportedInternal() {
93 android::base::unique_fd fd(art::memfd_create("test_android_memfd", MFD_ALLOW_SEALING));
94 if (fd == -1) {
95 LOG(INFO) << "memfd_create failed: " << strerror(errno) << ", no memfd support.";
96 return false;
97 }
98
99 if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE) == -1) {
100 LOG(INFO) << "fcntl(F_ADD_SEALS) failed: " << strerror(errno) << ", no memfd support.";
101 return false;
102 }
103
104 LOG(INFO) << "Using memfd for future sealing";
105 return true;
106 }
107
IsSealFutureWriteSupported()108 bool IsSealFutureWriteSupported() {
109 static bool is_seal_future_write_supported = IsSealFutureWriteSupportedInternal();
110 return is_seal_future_write_supported;
111 }
112
113 #else
114
IsSealFutureWriteSupported()115 bool IsSealFutureWriteSupported() {
116 return false;
117 }
118
119 #endif
120
121 } // namespace art
122