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 <glib.h> 31 #include <glib/gprintf.h> 32 33 #include <sys/mman.h> 34 35 #include "qemu/memfd.h" 36 37 #ifdef CONFIG_MEMFD 38 #include <sys/memfd.h> 39 #elif defined CONFIG_LINUX 40 #include <sys/syscall.h> 41 #include <asm/unistd.h> 42 43 static int memfd_create(const char *name, unsigned int flags) 44 { 45 #ifdef __NR_memfd_create 46 return syscall(__NR_memfd_create, name, flags); 47 #else 48 return -1; 49 #endif 50 } 51 #endif 52 53 #ifndef MFD_CLOEXEC 54 #define MFD_CLOEXEC 0x0001U 55 #endif 56 57 #ifndef MFD_ALLOW_SEALING 58 #define MFD_ALLOW_SEALING 0x0002U 59 #endif 60 61 /* 62 * This is a best-effort helper for shared memory allocation, with 63 * optional sealing. The helper will do his best to allocate using 64 * memfd with sealing, but may fallback on other methods without 65 * sealing. 66 */ 67 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals, 68 int *fd) 69 { 70 void *ptr; 71 int mfd = -1; 72 73 *fd = -1; 74 75 #ifdef CONFIG_LINUX 76 if (seals) { 77 mfd = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC); 78 } 79 80 if (mfd == -1) { 81 /* some systems have memfd without sealing */ 82 mfd = memfd_create(name, MFD_CLOEXEC); 83 seals = 0; 84 } 85 #endif 86 87 if (mfd != -1) { 88 if (ftruncate(mfd, size) == -1) { 89 perror("ftruncate"); 90 close(mfd); 91 return NULL; 92 } 93 94 if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) { 95 perror("fcntl"); 96 close(mfd); 97 return NULL; 98 } 99 } else { 100 const char *tmpdir = g_get_tmp_dir(); 101 gchar *fname; 102 103 fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir); 104 mfd = mkstemp(fname); 105 unlink(fname); 106 g_free(fname); 107 108 if (mfd == -1) { 109 perror("mkstemp"); 110 return NULL; 111 } 112 113 if (ftruncate(mfd, size) == -1) { 114 perror("ftruncate"); 115 close(mfd); 116 return NULL; 117 } 118 } 119 120 ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0); 121 if (ptr == MAP_FAILED) { 122 perror("mmap"); 123 close(mfd); 124 return NULL; 125 } 126 127 *fd = mfd; 128 return ptr; 129 } 130 131 void qemu_memfd_free(void *ptr, size_t size, int fd) 132 { 133 if (ptr) { 134 munmap(ptr, size); 135 } 136 137 if (fd != -1) { 138 close(fd); 139 } 140 } 141 142 enum { 143 MEMFD_KO, 144 MEMFD_OK, 145 MEMFD_TODO 146 }; 147 148 bool qemu_memfd_check(void) 149 { 150 static int memfd_check = MEMFD_TODO; 151 152 if (memfd_check == MEMFD_TODO) { 153 int fd; 154 void *ptr; 155 156 ptr = qemu_memfd_alloc("test", 4096, 0, &fd); 157 memfd_check = ptr ? MEMFD_OK : MEMFD_KO; 158 qemu_memfd_free(ptr, 4096, fd); 159 } 160 161 return memfd_check == MEMFD_OK; 162 } 163