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