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 <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 }