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/memfd.h" 32 #include "qemu/host-utils.h" 33 34 #if defined CONFIG_LINUX && !defined CONFIG_MEMFD 35 #include <sys/syscall.h> 36 #include <asm/unistd.h> 37 38 static int memfd_create(const char *name, unsigned int flags) 39 { 40 #ifdef __NR_memfd_create 41 return syscall(__NR_memfd_create, name, flags); 42 #else 43 errno = ENOSYS; 44 return -1; 45 #endif 46 } 47 #endif 48 49 int qemu_memfd_create(const char *name, size_t size, bool hugetlb, 50 uint64_t hugetlbsize, unsigned int seals, Error **errp) 51 { 52 int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0; 53 54 if (htsize && 1ULL << htsize != hugetlbsize) { 55 error_setg(errp, "Hugepage size must be a power of 2"); 56 return -1; 57 } 58 59 htsize = htsize << MFD_HUGE_SHIFT; 60 61 #ifdef CONFIG_LINUX 62 int mfd = -1; 63 unsigned int flags = MFD_CLOEXEC; 64 65 if (seals) { 66 flags |= MFD_ALLOW_SEALING; 67 } 68 if (hugetlb) { 69 flags |= MFD_HUGETLB; 70 flags |= htsize; 71 } 72 mfd = memfd_create(name, flags); 73 if (mfd < 0) { 74 error_setg_errno(errp, errno, 75 "failed to create memfd with flags 0x%x", flags); 76 goto err; 77 } 78 79 if (ftruncate(mfd, size) == -1) { 80 error_setg_errno(errp, errno, "failed to resize memfd to %zu", size); 81 goto err; 82 } 83 84 if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) { 85 error_setg_errno(errp, errno, "failed to add seals 0x%x", seals); 86 goto err; 87 } 88 89 return mfd; 90 91 err: 92 if (mfd >= 0) { 93 close(mfd); 94 } 95 #else 96 error_setg_errno(errp, ENOSYS, "failed to create memfd"); 97 #endif 98 return -1; 99 } 100 101 /* 102 * This is a best-effort helper for shared memory allocation, with 103 * optional sealing. The helper will do his best to allocate using 104 * memfd with sealing, but may fallback on other methods without 105 * sealing. 106 */ 107 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, 108 int *fd, Error **errp) 109 { 110 void *ptr; 111 int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL); 112 113 /* some systems have memfd without sealing */ 114 if (mfd == -1) { 115 mfd = qemu_memfd_create(name, size, false, 0, 0, NULL); 116 } 117 118 if (mfd == -1) { 119 const char *tmpdir = g_get_tmp_dir(); 120 gchar *fname; 121 122 fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir); 123 mfd = mkstemp(fname); 124 unlink(fname); 125 g_free(fname); 126 127 if (mfd == -1 || 128 ftruncate(mfd, size) == -1) { 129 goto err; 130 } 131 } 132 133 ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); 134 if (ptr == MAP_FAILED) { 135 goto err; 136 } 137 138 *fd = mfd; 139 return ptr; 140 141 err: 142 error_setg_errno(errp, errno, "failed to allocate shared memory"); 143 if (mfd >= 0) { 144 close(mfd); 145 } 146 return NULL; 147 } 148 149 void qemu_memfd_free(void *ptr, size_t size, int fd) 150 { 151 if (ptr) { 152 munmap(ptr, size); 153 } 154 155 if (fd != -1) { 156 close(fd); 157 } 158 } 159 160 enum { 161 MEMFD_KO, 162 MEMFD_OK, 163 MEMFD_TODO 164 }; 165 166 /** 167 * qemu_memfd_alloc_check(): 168 * 169 * Check if qemu_memfd_alloc() can allocate, including using a 170 * fallback implementation when host doesn't support memfd. 171 */ 172 bool qemu_memfd_alloc_check(void) 173 { 174 static int memfd_check = MEMFD_TODO; 175 176 if (memfd_check == MEMFD_TODO) { 177 int fd; 178 void *ptr; 179 180 fd = -1; 181 ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL); 182 memfd_check = ptr ? MEMFD_OK : MEMFD_KO; 183 qemu_memfd_free(ptr, 4096, fd); 184 } 185 186 return memfd_check == MEMFD_OK; 187 } 188 189 /** 190 * qemu_memfd_check(): 191 * 192 * Check if host supports memfd. 193 */ 194 bool qemu_memfd_check(unsigned int flags) 195 { 196 #ifdef CONFIG_LINUX 197 int mfd = memfd_create("test", flags | MFD_CLOEXEC); 198 199 if (mfd >= 0) { 200 close(mfd); 201 return true; 202 } 203 #endif 204 205 return false; 206 } 207