| 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. Cache the answer for the common case flags=0. |
| 198 | */ |
| 199 | bool qemu_memfd_check(unsigned int flags) |
| 200 | { |
| 201 | #ifdef CONFIG_LINUX |
| 202 | int mfd; |
| 203 | static int memfd_check = MEMFD_TODO; |
| 204 | |
| 205 | if (!flags && memfd_check != MEMFD_TODO) { |
| 206 | return memfd_check; |
| 207 | } |
| 208 | |
| 209 | mfd = memfd_create("test", flags | MFD_CLOEXEC); |
| 210 | if (mfd >= 0) { |
| 211 | close(mfd); |
| 212 | } |
| 213 | if (!flags) { |
| 214 | memfd_check = (mfd >= 0) ? MEMFD_OK : MEMFD_KO; |
| 215 | } |
| 216 | return (mfd >= 0); |
| 217 | |
| 218 | #endif |
| 219 | |
| 220 | return false; |
| 221 | } |