util/memfd.c

   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 "qemu/memfd.h"
  31
  32 #if defined CONFIG_LINUX && !defined CONFIG_MEMFD
  33 #include <sys/syscall.h>
  34 #include <asm/unistd.h>
  35
  36 static int memfd_create(const char *name, unsigned int flags)
  37 {
  38 #ifdef __NR_memfd_create
  39     return syscall(__NR_memfd_create, name, flags);
  40 #else
  41     return -1;
  42 #endif
  43 }
  44 #endif
  45
  46 #ifndef MFD_CLOEXEC
  47 #define MFD_CLOEXEC 0x0001U
  48 #endif
  49
  50 #ifndef MFD_ALLOW_SEALING
  51 #define MFD_ALLOW_SEALING 0x0002U
  52 #endif
  53
  54 int qemu_memfd_create(const char *name, size_t size, unsigned int seals)
  55 {
  56     int mfd = -1;
  57
  58 #ifdef CONFIG_LINUX
  59     unsigned int flags = MFD_CLOEXEC;
  60
  61     if (seals) {
  62         flags |= MFD_ALLOW_SEALING;
  63     }
  64
  65     mfd = memfd_create(name, flags);
  66     if (mfd < 0) {
  67         return -1;
  68     }
  69
  70     if (ftruncate(mfd, size) == -1) {
  71         perror("ftruncate");
  72         close(mfd);
  73         return -1;
  74     }
  75
  76     if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
  77         perror("fcntl");
  78         close(mfd);
  79         return -1;
  80     }
  81 #endif
  82
  83     return mfd;
  84 }
  85
  86 /*
  87  * This is a best-effort helper for shared memory allocation, with
  88  * optional sealing. The helper will do his best to allocate using
  89  * memfd with sealing, but may fallback on other methods without
  90  * sealing.
  91  */
  92 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
  93                        int *fd)
  94 {
  95     void *ptr;
  96     int mfd = qemu_memfd_create(name, size, seals);
  97
  98     /* some systems have memfd without sealing */
  99     if (mfd == -1) {
 100         mfd = qemu_memfd_create(name, size, 0);
 101     }
 102
 103     if (mfd == -1) {
 104         const char *tmpdir = g_get_tmp_dir();
 105         gchar *fname;
 106
 107         fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
 108         mfd = mkstemp(fname);
 109         unlink(fname);
 110         g_free(fname);
 111
 112         if (mfd == -1) {
 113             perror("mkstemp");
 114             return NULL;
 115         }
 116
 117         if (ftruncate(mfd, size) == -1) {
 118             perror("ftruncate");
 119             close(mfd);
 120             return NULL;
 121         }
 122     }
 123
 124     ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
 125     if (ptr == MAP_FAILED) {
 126         perror("mmap");
 127         close(mfd);
 128         return NULL;
 129     }
 130
 131     *fd = mfd;
 132     return ptr;
 133 }
 134
 135 void qemu_memfd_free(void *ptr, size_t size, int fd)
 136 {
 137     if (ptr) {
 138         munmap(ptr, size);
 139     }
 140
 141     if (fd != -1) {
 142         close(fd);
 143     }
 144 }
 145
 146 enum {
 147     MEMFD_KO,
 148     MEMFD_OK,
 149     MEMFD_TODO
 150 };
 151
 152 bool qemu_memfd_check(void)
 153 {
 154     static int memfd_check = MEMFD_TODO;
 155
 156     if (memfd_check == MEMFD_TODO) {
 157         int fd;
 158         void *ptr;
 159
 160         ptr = qemu_memfd_alloc("test", 4096, 0, &fd);
 161         memfd_check = ptr ? MEMFD_OK : MEMFD_KO;
 162         qemu_memfd_free(ptr, 4096, fd);
 163     }
 164
 165     return memfd_check == MEMFD_OK;
 166 }