LXR qemu/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
  40static 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 */
  64void *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
 128void 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
 139enum {
 140    MEMFD_KO,
 141    MEMFD_OK,
 142    MEMFD_TODO
 143};
 144
 145bool 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}
 160