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 return -1; 44 #endif 45 } 46 #endif 47 48 #ifndef MFD_CLOEXEC 49 #define MFD_CLOEXEC 0x0001U 50 #endif 51 52 #ifndef MFD_ALLOW_SEALING 53 #define MFD_ALLOW_SEALING 0x0002U 54 #endif 55 56 #ifndef MFD_HUGETLB 57 #define MFD_HUGETLB 0x0004U 58 #endif 59 60 #ifndef MFD_HUGE_SHIFT 61 #define MFD_HUGE_SHIFT 26 62 #endif 63 64 int qemu_memfd_create(const char *name, size_t size, bool hugetlb, 65 uint64_t hugetlbsize, unsigned int seals, Error **errp) 66 { 67 int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0; 68 69 if (htsize && 1ULL << htsize != hugetlbsize) { 70 error_setg(errp, "Hugepage size must be a power of 2"); 71 return -1; 72 } 73 74 htsize = htsize << MFD_HUGE_SHIFT; 75 76 #ifdef CONFIG_LINUX 77 int mfd = -1; 78 unsigned int flags = MFD_CLOEXEC; 79 80 if (seals) { 81 flags |= MFD_ALLOW_SEALING; 82 } 83 if (hugetlb) { 84 flags |= MFD_HUGETLB; 85 flags |= htsize; 86 } 87 mfd = memfd_create(name, flags); 88 if (mfd < 0) { 89 goto err; 90 } 91 92 if (ftruncate(mfd, size) == -1) { 93 goto err; 94 } 95 96 if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) { 97 goto err; 98 } 99 100 return mfd; 101 102 err: 103 if (mfd >= 0) { 104 close(mfd); 105 } 106 #endif 107 error_setg_errno(errp, errno, "failed to create memfd"); 108 return -1; 109 } 110 111 /* 112 * This is a best-effort helper for shared memory allocation, with 113 * optional sealing. The helper will do his best to allocate using 114 * memfd with sealing, but may fallback on other methods without 115 * sealing. 116 */ 117 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, 118 int *fd, Error **errp) 119 { 120 void *ptr; 121 int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL); 122 123 /* some systems have memfd without sealing */ 124 if (mfd == -1) { 125 mfd = qemu_memfd_create(name, size, false, 0, 0, NULL); 126 } 127 128 if (mfd == -1) { 129 const char *tmpdir = g_get_tmp_dir(); 130 gchar *fname; 131 132 fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir); 133 mfd = mkstemp(fname); 134 unlink(fname); 135 g_free(fname); 136 137 if (mfd == -1 || 138 ftruncate(mfd, size) == -1) { 139 goto err; 140 } 141 } 142 143 ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); 144 if (ptr == MAP_FAILED) { 145 goto err; 146 } 147 148 *fd = mfd; 149 return ptr; 150 151 err: 152 error_setg_errno(errp, errno, "failed to allocate shared memory"); 153 if (mfd >= 0) { 154 close(mfd); 155 } 156 return NULL; 157 } 158 159 void qemu_memfd_free(void *ptr, size_t size, int fd) 160 { 161 if (ptr) { 162 munmap(ptr, size); 163 } 164 165 if (fd != -1) { 166 close(fd); 167 } 168 } 169 170 enum { 171 MEMFD_KO, 172 MEMFD_OK, 173 MEMFD_TODO 174 }; 175 176 /** 177 * qemu_memfd_alloc_check(): 178 * 179 * Check if qemu_memfd_alloc() can allocate, including using a 180 * fallback implementation when host doesn't support memfd. 181 */ 182 bool qemu_memfd_alloc_check(void) 183 { 184 static int memfd_check = MEMFD_TODO; 185 186 if (memfd_check == MEMFD_TODO) { 187 int fd; 188 void *ptr; 189 190 ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL); 191 memfd_check = ptr ? MEMFD_OK : MEMFD_KO; 192 qemu_memfd_free(ptr, 4096, fd); 193 } 194 195 return memfd_check == MEMFD_OK; 196 } 197 198 /** 199 * qemu_memfd_check(): 200 * 201 * Check if host supports memfd. 202 */ 203 bool qemu_memfd_check(void) 204 { 205 #ifdef CONFIG_LINUX 206 static int memfd_check = MEMFD_TODO; 207 208 if (memfd_check == MEMFD_TODO) { 209 int mfd = memfd_create("test", 0); 210 if (mfd >= 0) { 211 memfd_check = MEMFD_OK; 212 close(mfd); 213 } else { 214 memfd_check = MEMFD_KO; 215 } 216 } 217 218 return memfd_check == MEMFD_OK; 219 #else 220 return false; 221 #endif 222 } 223