aboutsummaryrefslogtreecommitdiff
path: root/util/memfd.c
blob: b374238a59c121d409b369a0c5930a1dccba0f7a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
/*
 * memfd.c
 *
 * Copyright (c) 2015 Red Hat, Inc.
 *
 * QEMU library functions on POSIX which are shared between QEMU and
 * the QEMU tools.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "qemu/osdep.h"

#include <glib/gprintf.h>

#include <sys/mman.h>

#include "qemu/memfd.h"

#ifdef CONFIG_MEMFD
#include <sys/memfd.h>
#elif defined CONFIG_LINUX
#include <sys/syscall.h>
#include <asm/unistd.h>

static int memfd_create(const char *name, unsigned int flags)
{
#ifdef __NR_memfd_create
    return syscall(__NR_memfd_create, name, flags);
#else
    return -1;
#endif
}
#endif

#ifndef MFD_CLOEXEC
#define MFD_CLOEXEC 0x0001U
#endif

#ifndef MFD_ALLOW_SEALING
#define MFD_ALLOW_SEALING 0x0002U
#endif

/*
 * This is a best-effort helper for shared memory allocation, with
 * optional sealing. The helper will do his best to allocate using
 * memfd with sealing, but may fallback on other methods without
 * sealing.
 */
void *qemu_memfd_alloc(const char *name, size_t size, unsigned int seals,
                       int *fd)
{
    void *ptr;
    int mfd = -1;

    *fd = -1;

#ifdef CONFIG_LINUX
    if (seals) {
        mfd = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
    }

    if (mfd == -1) {
        /* some systems have memfd without sealing */
        mfd = memfd_create(name, MFD_CLOEXEC);
        seals = 0;
    }
#endif

    if (mfd != -1) {
        if (ftruncate(mfd, size) == -1) {
            perror("ftruncate");
            close(mfd);
            return NULL;
        }

        if (seals && fcntl(mfd, F_ADD_SEALS, seals) == -1) {
            perror("fcntl");
            close(mfd);
            return NULL;
        }
    } else {
        const char *tmpdir = g_get_tmp_dir();
        gchar *fname;

        fname = g_strdup_printf("%s/memfd-XXXXXX", tmpdir);
        mfd = mkstemp(fname);
        unlink(fname);
        g_free(fname);

        if (mfd == -1) {
            perror("mkstemp");
            return NULL;
        }

        if (ftruncate(mfd, size) == -1) {
            perror("ftruncate");
            close(mfd);
            return NULL;
        }
    }

    ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
    if (ptr == MAP_FAILED) {
        perror("mmap");
        close(mfd);
        return NULL;
    }

    *fd = mfd;
    return ptr;
}

void qemu_memfd_free(void *ptr, size_t size, int fd)
{
    if (ptr) {
        munmap(ptr, size);
    }

    if (fd != -1) {
        close(fd);
    }
}

enum {
    MEMFD_KO,
    MEMFD_OK,
    MEMFD_TODO
};

bool qemu_memfd_check(void)
{
    static int memfd_check = MEMFD_TODO;

    if (memfd_check == MEMFD_TODO) {
        int fd;
        void *ptr;

        ptr = qemu_memfd_alloc("test", 4096, 0, &fd);
        memfd_check = ptr ? MEMFD_OK : MEMFD_KO;
        qemu_memfd_free(ptr, 4096, fd);
    }

    return memfd_check == MEMFD_OK;
}