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