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 | } |
207 | |