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
37 // When building for linux host, glibc in prebuilts does not include memfd_create system call
38 // number. As a temporary testing measure, we add the definition here.
39 #if defined(__linux__) && !defined(__NR_memfd_create)
40 #if defined(__x86_64__)
41 #define __NR_memfd_create 319
42 #elif defined(__i386__)
43 #define __NR_memfd_create 356
44 #endif // defined(__i386__)
45 #endif // defined(__linux__) && !defined(__NR_memfd_create)
46
47 namespace art {
48
49 #if defined(__NR_memfd_create)
50
memfd_create(const char * name,unsigned int flags)51 int memfd_create(const char* name, unsigned int flags) {
52 // Check kernel version supports memfd_create(). Some older kernels segfault executing
53 // memfd_create() rather than returning ENOSYS (b/116769556).
54 static constexpr int kRequiredMajor = 3;
55 static constexpr int kRequiredMinor = 17;
56 struct utsname uts;
57 int major, minor;
58 if (uname(&uts) != 0 ||
59 strcmp(uts.sysname, "Linux") != 0 ||
60 sscanf(uts.release, "%d.%d", &major, &minor) != 2 ||
61 (major < kRequiredMajor || (major == kRequiredMajor && minor < kRequiredMinor))) {
62 errno = ENOSYS;
63 return -1;
64 }
65
66 return syscall(__NR_memfd_create, name, flags);
67 }
68
69 #else // __NR_memfd_create
70
71 int memfd_create(const char* name ATTRIBUTE_UNUSED, unsigned int flags ATTRIBUTE_UNUSED) {
72 errno = ENOSYS;
73 return -1;
74 }
75
76 #endif // __NR_memfd_create
77
78 // This is a wrapper that will attempt to simulate memfd_create if normal running fails.
memfd_create_compat(const char * name,unsigned int flags)79 int memfd_create_compat(const char* name, unsigned int flags) {
80 int res = memfd_create(name, flags);
81 if (res >= 0) {
82 return res;
83 }
84 #if !defined(_WIN32)
85 // Try to create an anonymous file with tmpfile that we can use instead.
86 if (flags == 0) {
87 FILE* file = tmpfile();
88 if (file != nullptr) {
89 // We want the normal 'dup' semantics since memfd_create without any flags isn't CLOEXEC.
90 // Unfortunately on some android targets we will compiler error if we use dup directly and so
91 // need to use fcntl.
92 int nfd = fcntl(fileno(file), F_DUPFD, /*lowest allowed fd*/ 0);
93 fclose(file);
94 return nfd;
95 }
96 }
97 #endif
98 return res;
99 }
100
101 #if defined(__BIONIC__)
102
IsSealFutureWriteSupportedInternal()103 static bool IsSealFutureWriteSupportedInternal() {
104 android::base::unique_fd fd(art::memfd_create("test_android_memfd", MFD_ALLOW_SEALING));
105 if (fd == -1) {
106 LOG(INFO) << "memfd_create failed: " << strerror(errno) << ", no memfd support.";
107 return false;
108 }
109
110 if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE) == -1) {
111 LOG(INFO) << "fcntl(F_ADD_SEALS) failed: " << strerror(errno) << ", no memfd support.";
112 return false;
113 }
114
115 LOG(INFO) << "Using memfd for future sealing";
116 return true;
117 }
118
IsSealFutureWriteSupported()119 bool IsSealFutureWriteSupported() {
120 static bool is_seal_future_write_supported = IsSealFutureWriteSupportedInternal();
121 return is_seal_future_write_supported;
122 }
123
124 #else
125
IsSealFutureWriteSupported()126 bool IsSealFutureWriteSupported() {
127 return false;
128 }
129
130 #endif
131
132 } // namespace art
133