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