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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "memfd.h"
#include <errno.h>
#include <stdio.h>
#if !defined(_WIN32)
#include <fcntl.h>
#include <sys/syscall.h>
#include <sys/utsname.h>
#include <unistd.h>
#endif
#if defined(__BIONIC__)
#include <linux/memfd.h> // To access memfd flags.
#endif
#include <android-base/logging.h>
#include <android-base/unique_fd.h>
#include <cstring>
#include "macros.h"
// When building for linux host, glibc in prebuilts does not include memfd_create system call
// number. As a temporary testing measure, we add the definition here.
#if defined(__linux__) && !defined(__NR_memfd_create)
#if defined(__x86_64__)
#define __NR_memfd_create 319
#elif defined(__i386__)
#define __NR_memfd_create 356
#endif // defined(__i386__)
#endif // defined(__linux__) && !defined(__NR_memfd_create)
namespace art {
#if defined(__NR_memfd_create)
int memfd_create(const char* name, unsigned int flags) {
// Check kernel version supports memfd_create(). Some older kernels segfault executing
// memfd_create() rather than returning ENOSYS (b/116769556).
static constexpr int kRequiredMajor = 3;
static constexpr int kRequiredMinor = 17;
struct utsname uts;
int major, minor;
if (uname(&uts) != 0 ||
strcmp(uts.sysname, "Linux") != 0 ||
sscanf(uts.release, "%d.%d", &major, &minor) != 2 ||
(major < kRequiredMajor || (major == kRequiredMajor && minor < kRequiredMinor))) {
errno = ENOSYS;
return -1;
}
return syscall(__NR_memfd_create, name, flags);
}
#else // __NR_memfd_create
int memfd_create(const char* name ATTRIBUTE_UNUSED, unsigned int flags ATTRIBUTE_UNUSED) {
errno = ENOSYS;
return -1;
}
#endif // __NR_memfd_create
// This is a wrapper that will attempt to simulate memfd_create if normal running fails.
int memfd_create_compat(const char* name, unsigned int flags) {
int res = memfd_create(name, flags);
if (res >= 0) {
return res;
}
#if !defined(_WIN32)
// Try to create an anonymous file with tmpfile that we can use instead.
if (flags == 0) {
FILE* file = tmpfile();
if (file != nullptr) {
// We want the normal 'dup' semantics since memfd_create without any flags isn't CLOEXEC.
// Unfortunately on some android targets we will compiler error if we use dup directly and so
// need to use fcntl.
int nfd = fcntl(fileno(file), F_DUPFD, /*lowest allowed fd*/ 0);
fclose(file);
return nfd;
}
}
#endif
return res;
}
#if defined(__BIONIC__)
static bool IsSealFutureWriteSupportedInternal() {
android::base::unique_fd fd(art::memfd_create("test_android_memfd", MFD_ALLOW_SEALING));
if (fd == -1) {
LOG(INFO) << "memfd_create failed: " << strerror(errno) << ", no memfd support.";
return false;
}
if (fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE) == -1) {
LOG(INFO) << "fcntl(F_ADD_SEALS) failed: " << strerror(errno) << ", no memfd support.";
return false;
}
LOG(INFO) << "Using memfd for future sealing";
return true;
}
bool IsSealFutureWriteSupported() {
static bool is_seal_future_write_supported = IsSealFutureWriteSupportedInternal();
return is_seal_future_write_supported;
}
#else
bool IsSealFutureWriteSupported() {
return false;
}
#endif
} // namespace art
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