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 "qapi/error.h"
  31 #include "qemu/memfd.h"
  32 #include "qemu/host-utils.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 int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
  49                       uint64_t hugetlbsize, unsigned int seals, Error **errp)
  50 {
  51     int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
  52
  53     if (htsize && 1ULL << htsize != hugetlbsize) {
  54         error_setg(errp, "Hugepage size must be a power of 2");
  55         return -1;
  56     }
  57
  58     htsize = htsize << MFD_HUGE_SHIFT;
  59
  60 #ifdef CONFIG_LINUX
  61     int mfd = -1;
  62     unsigned int flags = MFD_CLOEXEC;
  63
  64     if (seals) {
  65         flags |= MFD_ALLOW_SEALING;
  66     }
  67     if (hugetlb) {
  68         flags |= MFD_HUGETLB;
  69         flags |= htsize;
  70     }
  71     mfd = memfd_create(name, flags);
  72     if (mfd < 0) {
  73         goto err;
  74     }
  75
  76     if (ftruncate(mfd, size) == -1) {
  77         goto err;
  78     }
  79
  80     if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
  81         goto err;
  82     }
  83
  84     return mfd;
  85
  86 err:
  87     if (mfd >= 0) {
  88         close(mfd);
  89     }
  90 #endif
  91     error_setg_errno(errp, errno, "failed to create memfd");
  92     return -1;
  93 }
  94
  95 /*
  96  * This is a best-effort helper for shared memory allocation, with
  97  * optional sealing. The helper will do his best to allocate using
  98  * memfd with sealing, but may fallback on other methods without
  99  * sealing.
 100  */
 101 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
 102                        int *fd, Error **errp)
 103 {
 104     void *ptr;
 105     int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL);
 106
 107     /* some systems have memfd without sealing */
 108     if (mfd == -1) {
 109         mfd = qemu_memfd_create(name, size, false, 0, 0, NULL);
 110     }
 111
 112     if (mfd == -1) {
 113         const char *tmpdir = g_get_tmp_dir();
 114         gchar *fname;
 115
 116         fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
 117         mfd = mkstemp(fname);
 118         unlink(fname);
 119         g_free(fname);
 120
 121         if (mfd == -1 ||
 122             ftruncate(mfd, size) == -1) {
 123             goto err;
 124         }
 125     }
 126
 127     ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
 128     if (ptr == MAP_FAILED) {
 129         goto err;
 130     }
 131
 132     *fd = mfd;
 133     return ptr;
 134
 135 err:
 136     error_setg_errno(errp, errno, "failed to allocate shared memory");
 137     if (mfd >= 0) {
 138         close(mfd);
 139     }
 140     return NULL;
 141 }
 142
 143 void qemu_memfd_free(void *ptr, size_t size, int fd)
 144 {
 145     if (ptr) {
 146         munmap(ptr, size);
 147     }
 148
 149     if (fd != -1) {
 150         close(fd);
 151     }
 152 }
 153
 154 enum {
 155     MEMFD_KO,
 156     MEMFD_OK,
 157     MEMFD_TODO
 158 };
 159
 160 /**
 161  * qemu_memfd_alloc_check():
 162  *
 163  * Check if qemu_memfd_alloc() can allocate, including using a
 164  * fallback implementation when host doesn't support memfd.
 165  */
 166 bool qemu_memfd_alloc_check(void)
 167 {
 168     static int memfd_check = MEMFD_TODO;
 169
 170     if (memfd_check == MEMFD_TODO) {
 171         int fd;
 172         void *ptr;
 173
 174         fd = -1;
 175         ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL);
 176         memfd_check = ptr ? MEMFD_OK : MEMFD_KO;
 177         qemu_memfd_free(ptr, 4096, fd);
 178     }
 179
 180     return memfd_check == MEMFD_OK;
 181 }
 182
 183 /**
 184  * qemu_memfd_check():
 185  *
 186  * Check if host supports memfd.
 187  */
 188 bool qemu_memfd_check(unsigned int flags)
 189 {
 190 #ifdef CONFIG_LINUX
 191     int mfd = memfd_create("test", flags);
 192
 193     if (mfd >= 0) {
 194         close(mfd);
 195         return true;
 196     }
 197 #endif
 198
 199     return false;
 200 }