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     errno = ENOSYS;
  44     return -1;
  45 #endif
  46 }
  47 #endif
  48
  49 int qemu_memfd_create(const char *name, size_t size, bool hugetlb,
  50                       uint64_t hugetlbsize, unsigned int seals, Error **errp)
  51 {
  52     int htsize = hugetlbsize ? ctz64(hugetlbsize) : 0;
  53
  54     if (htsize && 1ULL << htsize != hugetlbsize) {
  55         error_setg(errp, "Hugepage size must be a power of 2");
  56         return -1;
  57     }
  58
  59     htsize = htsize << MFD_HUGE_SHIFT;
  60
  61 #ifdef CONFIG_LINUX
  62     int mfd = -1;
  63     unsigned int flags = MFD_CLOEXEC;
  64
  65     if (seals) {
  66         flags |= MFD_ALLOW_SEALING;
  67     }
  68     if (hugetlb) {
  69         flags |= MFD_HUGETLB;
  70         flags |= htsize;
  71     }
  72     mfd = memfd_create(name, flags);
  73     if (mfd < 0) {
  74         error_setg_errno(errp, errno,
  75                          "failed to create memfd with flags 0x%x", flags);
  76         goto err;
  77     }
  78
  79     if (ftruncate(mfd, size) == -1) {
  80         error_setg_errno(errp, errno, "failed to resize memfd to %zu", size);
  81         goto err;
  82     }
  83
  84     if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
  85         error_setg_errno(errp, errno, "failed to add seals 0x%x", seals);
  86         goto err;
  87     }
  88
  89     return mfd;
  90
  91 err:
  92     if (mfd >= 0) {
  93         close(mfd);
  94     }
  95 #else
  96     error_setg_errno(errp, ENOSYS, "failed to create memfd");
  97 #endif
  98     return -1;
  99 }
 100
 101 /*
 102  * This is a best-effort helper for shared memory allocation, with
 103  * optional sealing. The helper will do his best to allocate using
 104  * memfd with sealing, but may fallback on other methods without
 105  * sealing.
 106  */
 107 void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
 108                        int *fd, Error **errp)
 109 {
 110     void *ptr;
 111     int mfd = qemu_memfd_create(name, size, false, 0, seals, NULL);
 112
 113     /* some systems have memfd without sealing */
 114     if (mfd == -1) {
 115         mfd = qemu_memfd_create(name, size, false, 0, 0, NULL);
 116     }
 117
 118     if (mfd == -1) {
 119         const char *tmpdir = g_get_tmp_dir();
 120         gchar *fname;
 121
 122         fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
 123         mfd = mkstemp(fname);
 124         unlink(fname);
 125         g_free(fname);
 126
 127         if (mfd == -1 ||
 128             ftruncate(mfd, size) == -1) {
 129             goto err;
 130         }
 131     }
 132
 133     ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
 134     if (ptr == MAP_FAILED) {
 135         goto err;
 136     }
 137
 138     *fd = mfd;
 139     return ptr;
 140
 141 err:
 142     error_setg_errno(errp, errno, "failed to allocate shared memory");
 143     if (mfd >= 0) {
 144         close(mfd);
 145     }
 146     return NULL;
 147 }
 148
 149 void qemu_memfd_free(void *ptr, size_t size, int fd)
 150 {
 151     if (ptr) {
 152         munmap(ptr, size);
 153     }
 154
 155     if (fd != -1) {
 156         close(fd);
 157     }
 158 }
 159
 160 enum {
 161     MEMFD_KO,
 162     MEMFD_OK,
 163     MEMFD_TODO
 164 };
 165
 166 /**
 167  * qemu_memfd_alloc_check():
 168  *
 169  * Check if qemu_memfd_alloc() can allocate, including using a
 170  * fallback implementation when host doesn't support memfd.
 171  */
 172 bool qemu_memfd_alloc_check(void)
 173 {
 174     static int memfd_check = MEMFD_TODO;
 175
 176     if (memfd_check == MEMFD_TODO) {
 177         int fd;
 178         void *ptr;
 179
 180         fd = -1;
 181         ptr = qemu_memfd_alloc("test", 4096, 0, &fd, NULL);
 182         memfd_check = ptr ? MEMFD_OK : MEMFD_KO;
 183         qemu_memfd_free(ptr, 4096, fd);
 184     }
 185
 186     return memfd_check == MEMFD_OK;
 187 }
 188
 189 /**
 190  * qemu_memfd_check():
 191  *
 192  * Check if host supports memfd.
 193  */
 194 bool qemu_memfd_check(unsigned int flags)
 195 {
 196 #ifdef CONFIG_LINUX
 197     int mfd = memfd_create("test", flags | MFD_CLOEXEC);
 198
 199     if (mfd >= 0) {
 200         close(mfd);
 201         return true;
 202     }
 203 #endif
 204
 205     return false;
 206 }