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 "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 }