1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright IBM Corporation, 2021
4 *
5 * Author: Mike Rapoport <rppt@linux.ibm.com>
6 */
7
8 #include <linux/mm.h>
9 #include <linux/fs.h>
10 #include <linux/swap.h>
11 #include <linux/mount.h>
12 #include <linux/memfd.h>
13 #include <linux/bitops.h>
14 #include <linux/printk.h>
15 #include <linux/pagemap.h>
16 #include <linux/syscalls.h>
17 #include <linux/pseudo_fs.h>
18 #include <linux/secretmem.h>
19 #include <linux/set_memory.h>
20 #include <linux/sched/signal.h>
21
22 #include <uapi/linux/magic.h>
23
24 #include <asm/tlbflush.h>
25
26 #include "internal.h"
27
28 #undef pr_fmt
29 #define pr_fmt(fmt) "secretmem: " fmt
30
31 /*
32 * Define mode and flag masks to allow validation of the system call
33 * parameters.
34 */
35 #define SECRETMEM_MODE_MASK (0x0)
36 #define SECRETMEM_FLAGS_MASK SECRETMEM_MODE_MASK
37
38 static bool secretmem_enable __ro_after_init = 1;
39 module_param_named(enable, secretmem_enable, bool, 0400);
40 MODULE_PARM_DESC(secretmem_enable,
41 "Enable secretmem and memfd_secret(2) system call");
42
43 static atomic_t secretmem_users;
44
45 bool secretmem_active(void)
46 {
47 return !!atomic_read(&secretmem_users);
48 }
49
50 static vm_fault_t secretmem_fault(struct vm_fault *vmf)
51 {
52 struct address_space *mapping = vmf->vma->vm_file->f_mapping;
53 struct inode *inode = file_inode(vmf->vma->vm_file);
54 pgoff_t offset = vmf->pgoff;
55 gfp_t gfp = vmf->gfp_mask;
56 unsigned long addr;
57 struct page *page;
58 struct folio *folio;
59 vm_fault_t ret;
60 int err;
61
62 if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
63 return vmf_error(-EINVAL);
64
65 filemap_invalidate_lock_shared(mapping);
66
67 retry:
68 page = find_lock_page(mapping, offset);
69 if (!page) {
70 folio = folio_alloc(gfp | __GFP_ZERO, 0);
71 if (!folio) {
72 ret = VM_FAULT_OOM;
73 goto out;
74 }
75
76 page = &folio->page;
77 err = set_direct_map_invalid_noflush(page);
78 if (err) {
79 folio_put(folio);
80 ret = vmf_error(err);
81 goto out;
82 }
83
84 __folio_mark_uptodate(folio);
85 err = filemap_add_folio(mapping, folio, offset, gfp);
86 if (unlikely(err)) {
87 folio_put(folio);
88 /*
89 * If a split of large page was required, it
90 * already happened when we marked the page invalid
91 * which guarantees that this call won't fail
92 */
93 set_direct_map_default_noflush(page);
94 if (err == -EEXIST)
95 goto retry;
96
97 ret = vmf_error(err);
98 goto out;
99 }
100
101 addr = (unsigned long)page_address(page);
102 flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
103 }
104
105 vmf->page = page;
106 ret = VM_FAULT_LOCKED;
107
108 out:
109 filemap_invalidate_unlock_shared(mapping);
110 return ret;
111 }
112
113 static const struct vm_operations_struct secretmem_vm_ops = {
114 .fault = secretmem_fault,
115 };
116
117 static int secretmem_release(struct inode *inode, struct file *file)
118 {
119 atomic_dec(&secretmem_users);
120 return 0;
121 }
122
123 static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
124 {
125 unsigned long len = vma->vm_end - vma->vm_start;
126
127 if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
128 return -EINVAL;
129
130 if (!mlock_future_ok(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
131 return -EAGAIN;
132
133 vm_flags_set(vma, VM_LOCKED | VM_DONTDUMP);
134 vma->vm_ops = &secretmem_vm_ops;
135
136 return 0;
137 }
138
139 bool vma_is_secretmem(struct vm_area_struct *vma)
140 {
141 return vma->vm_ops == &secretmem_vm_ops;
142 }
143
144 static const struct file_operations secretmem_fops = {
145 .release = secretmem_release,
146 .mmap = secretmem_mmap,
147 };
148
149 static int secretmem_migrate_folio(struct address_space *mapping,
150 struct folio *dst, struct folio *src, enum migrate_mode mode)
151 {
152 return -EBUSY;
153 }
154
155 static void secretmem_free_folio(struct folio *folio)
156 {
157 set_direct_map_default_noflush(&folio->page);
158 folio_zero_segment(folio, 0, folio_size(folio));
159 }
160
161 const struct address_space_operations secretmem_aops = {
162 .dirty_folio = noop_dirty_folio,
163 .free_folio = secretmem_free_folio,
164 .migrate_folio = secretmem_migrate_folio,
165 };
166
167 static int secretmem_setattr(struct mnt_idmap *idmap,
168 struct dentry *dentry, struct iattr *iattr)
169 {
170 struct inode *inode = d_inode(dentry);
171 struct address_space *mapping = inode->i_mapping;
172 unsigned int ia_valid = iattr->ia_valid;
173 int ret;
174
175 filemap_invalidate_lock(mapping);
176
177 if ((ia_valid & ATTR_SIZE) && inode->i_size)
178 ret = -EINVAL;
179 else
180 ret = simple_setattr(idmap, dentry, iattr);
181
182 filemap_invalidate_unlock(mapping);
183
184 return ret;
185 }
186
187 static const struct inode_operations secretmem_iops = {
188 .setattr = secretmem_setattr,
189 };
190
191 static struct vfsmount *secretmem_mnt;
192
193 static struct file *secretmem_file_create(unsigned long flags)
194 {
195 struct file *file;
196 struct inode *inode;
197 const char *anon_name = "[secretmem]";
198 const struct qstr qname = QSTR_INIT(anon_name, strlen(anon_name));
199 int err;
200
201 inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
202 if (IS_ERR(inode))
203 return ERR_CAST(inode);
204
205 err = security_inode_init_security_anon(inode, &qname, NULL);
206 if (err) {
207 file = ERR_PTR(err);
208 goto err_free_inode;
209 }
210
211 file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
212 O_RDWR, &secretmem_fops);
213 if (IS_ERR(file))
214 goto err_free_inode;
215
216 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
217 mapping_set_unevictable(inode->i_mapping);
218
219 inode->i_op = &secretmem_iops;
220 inode->i_mapping->a_ops = &secretmem_aops;
221
222 /* pretend we are a normal file with zero size */
223 inode->i_mode |= S_IFREG;
224 inode->i_size = 0;
225
226 return file;
227
228 err_free_inode:
229 iput(inode);
230 return file;
231 }
232
233 SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
234 {
235 struct file *file;
236 int fd, err;
237
238 /* make sure local flags do not confict with global fcntl.h */
239 BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
240
241 if (!secretmem_enable || !can_set_direct_map())
242 return -ENOSYS;
243
244 if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
245 return -EINVAL;
246 if (atomic_read(&secretmem_users) < 0)
247 return -ENFILE;
248
249 fd = get_unused_fd_flags(flags & O_CLOEXEC);
250 if (fd < 0)
251 return fd;
252
253 file = secretmem_file_create(flags);
254 if (IS_ERR(file)) {
255 err = PTR_ERR(file);
256 goto err_put_fd;
257 }
258
259 file->f_flags |= O_LARGEFILE;
260
261 atomic_inc(&secretmem_users);
262 fd_install(fd, file);
263 return fd;
264
265 err_put_fd:
266 put_unused_fd(fd);
267 return err;
268 }
269
270 static int secretmem_init_fs_context(struct fs_context *fc)
271 {
272 return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
273 }
274
275 static struct file_system_type secretmem_fs = {
276 .name = "secretmem",
277 .init_fs_context = secretmem_init_fs_context,
278 .kill_sb = kill_anon_super,
279 };
280
281 static int __init secretmem_init(void)
282 {
283 if (!secretmem_enable || !can_set_direct_map())
284 return 0;
285
286 secretmem_mnt = kern_mount(&secretmem_fs);
287 if (IS_ERR(secretmem_mnt))
288 return PTR_ERR(secretmem_mnt);
289
290 /* prevent secretmem mappings from ever getting PROT_EXEC */
291 secretmem_mnt->mnt_flags |= MNT_NOEXEC;
292
293 return 0;
294 }
295 fs_initcall(secretmem_init);
296
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