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