1 /* 2 * memfd.c 3 * 4 * Copyright (c) 2015 Red Hat, Inc. 5 * 6 * QEMU library functions on POSIX which are shared between QEMU and 7 * the QEMU tools. 8 * 9 * Permission is hereby granted, free of charge, to any person obtaining a copy 10 * of this software and associated documentation files (the "Software"), to deal 11 * in the Software without restriction, including without limitation the rights 12 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 13 * copies of the Software, and to permit persons to whom the Software is 14 * furnished to do so, subject to the following conditions: 15 * 16 * The above copyright notice and this permission notice shall be included in 17 * all copies or substantial portions of the Software. 18 * 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 20 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 21 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 22 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 23 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 24 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 25 * THE SOFTWARE. 26 */ 27 28 #include "qemu/osdep.h" 29 30 #include "qapi/error.h" 31 #include "qemu/error-report.h" 32 #include "qemu/memfd.h" 33 #include "qemu/host-utils.h" 34 35 #if defined CONFIG_LINUX && !defined CONFIG_MEMFD 36 #include <sys/syscall.h> 37 #include <asm/unistd.h> 38 39 int memfd_create(const char *name, unsigned int flags) 40 { 41 #ifdef __NR_memfd_create 42 return syscall(__NR_memfd_create, name, flags); 43 #else 44 errno = ENOSYS; 45 return -1; 46 #endif 47 } 48 #endif 49 50 int qemu_memfd_create(const char *name, size_t size, bool hugetlb, 51 uint64_t hugetlbsize, unsigned int seals, Error **errp) 52 { 53 int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0; 54 55 if (htsize && 1ULL << htsize != hugetlbsize) { 56 error_setg(errp, "Hugepage size must be a power of 2"); 57 return -1; 58 } 59 60 htsize = htsize << MFD_HUGE_SHIFT; 61 62 #ifdef CONFIG_LINUX 63 int mfd = -1; 64 unsigned int flags = MFD_CLOEXEC; 65 66 if (seals) { 67 flags |= MFD_ALLOW_SEALING; 68 } 69 if (hugetlb) { 70 flags |= MFD_HUGETLB; 71 flags |= htsize; 72 } 73 mfd = memfd_create(name, flags); 74 if (mfd < 0) { 75 error_setg_errno(errp, errno, 76 "failed to create memfd with flags 0x%x", flags); 77 goto err; 78 } 79 80 if (ftruncate(mfd, size) == -1) { 81 error_setg_errno(errp, errno, "failed to resize memfd to %zu", size); 82 goto err; 83 } 84 85 if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) { 86 error_setg_errno(errp, errno, "failed to add seals 0x%x", seals); 87 goto err; 88 } 89 90 return mfd; 91 92 err: 93 if (mfd >= 0) { 94 close(mfd); 95 } 96 #else 97 error_setg_errno(errp, ENOSYS, "failed to create memfd"); 98 #endif 99 return -1; 100 } 101 102 /* 103 * This is a best-effort helper for shared memory allocation, with 104 * optional sealing. The helper will do his best to allocate using 105 * memfd with sealing, but may fallback on other methods without 106 * sealing. 107 */ 108 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, 109 int *fd, Error **errp) 110 { 111 void *ptr; 112 int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL); 113 114 /* some systems have memfd without sealing */ 115 if (mfd == -1) { 116 mfd = qemu_memfd_create(name, size, false, 0, 0, NULL); 117 } 118 119 if (mfd == -1) { 120 const char *tmpdir = g_get_tmp_dir(); 121 gchar *fname; 122 123 fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir); 124 mfd = mkstemp(fname); 125 unlink(fname); 126 g_free(fname); 127 128 if (mfd == -1 || 129 ftruncate(mfd, size) == -1) { 130 goto err; 131 } 132 } 133 134 ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); 135 if (ptr == MAP_FAILED) { 136 goto err; 137 } 138 139 *fd = mfd; 140 return ptr; 141 142 err: 143 error_setg_errno(errp, errno, "failed to allocate shared memory"); 144 if (mfd >= 0) { 145 close(mfd); 146 } 147 return NULL; 148 } 149 150 void qemu_memfd_free(void *ptr, size_t size, int fd) 151 { 152 if (ptr) { 153 if (munmap(ptr, size) != 0) { 154 error_report("memfd munmap() failed: %s", strerror(errno)); 155 } 156 } 157 158 if (fd != -1) { 159 if (close(fd) != 0) { 160 error_report("memfd close() failed: %s", strerror(errno)); 161 } 162 } 163 } 164 165 enum { 166 MEMFD_KO, 167 MEMFD_OK, 168 MEMFD_TODO 169 }; 170 171 /** 172 * qemu_memfd_alloc_check(): 173 * 174 * Check if qemu_memfd_alloc() can allocate, including using a 175 * fallback implementation when host doesn't support memfd. 176 */ 177 bool qemu_memfd_alloc_check(void) 178 { 179 static int memfd_check = MEMFD_TODO; 180 181 if (memfd_check == MEMFD_TODO) { 182 int fd; 183 void *ptr; 184 185 fd = -1; 186 ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL); 187 memfd_check = ptr ? MEMFD_OK : MEMFD_KO; 188 qemu_memfd_free(ptr, 4096, fd); 189 } 190 191 return memfd_check == MEMFD_OK; 192 } 193 194 /** 195 * qemu_memfd_check(): 196 * 197 * Check if host supports memfd. 198 */ 199 bool qemu_memfd_check(unsigned int flags) 200 { 201 #ifdef CONFIG_LINUX 202 int mfd = memfd_create("test", flags | MFD_CLOEXEC); 203 204 if (mfd >= 0) { 205 close(mfd); 206 return true; 207 } 208 #endif 209 210 return false; 211 } 212