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/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 }