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;
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
secretmem_active(void)45 bool secretmem_active(void)
46 {
47 return !!atomic_read(&secretmem_users);
48 }
49
secretmem_fault(struct vm_fault * vmf)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 vm_fault_t ret;
59 int err;
60
61 if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
62 return vmf_error(-EINVAL);
63
64 filemap_invalidate_lock_shared(mapping);
65
66 retry:
67 page = find_lock_page(mapping, offset);
68 if (!page) {
69 page = alloc_page(gfp | __GFP_ZERO);
70 if (!page) {
71 ret = VM_FAULT_OOM;
72 goto out;
73 }
74
75 err = set_direct_map_invalid_noflush(page);
76 if (err) {
77 put_page(page);
78 ret = vmf_error(err);
79 goto out;
80 }
81
82 __SetPageUptodate(page);
83 err = add_to_page_cache_lru(page, mapping, offset, gfp);
84 if (unlikely(err)) {
85 put_page(page);
86 /*
87 * If a split of large page was required, it
88 * already happened when we marked the page invalid
89 * which guarantees that this call won't fail
90 */
91 set_direct_map_default_noflush(page);
92 if (err == -EEXIST)
93 goto retry;
94
95 ret = vmf_error(err);
96 goto out;
97 }
98
99 addr = (unsigned long)page_address(page);
100 flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
101 }
102
103 vmf->page = page;
104 ret = VM_FAULT_LOCKED;
105
106 out:
107 filemap_invalidate_unlock_shared(mapping);
108 return ret;
109 }
110
111 static const struct vm_operations_struct secretmem_vm_ops = {
112 .fault = secretmem_fault,
113 };
114
secretmem_release(struct inode * inode,struct file * file)115 static int secretmem_release(struct inode *inode, struct file *file)
116 {
117 atomic_dec(&secretmem_users);
118 return 0;
119 }
120
secretmem_mmap(struct file * file,struct vm_area_struct * vma)121 static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
122 {
123 unsigned long len = vma->vm_end - vma->vm_start;
124
125 if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
126 return -EINVAL;
127
128 if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
129 return -EAGAIN;
130
131 vma->vm_flags |= VM_LOCKED | VM_DONTDUMP;
132 vma->vm_ops = &secretmem_vm_ops;
133
134 return 0;
135 }
136
vma_is_secretmem(struct vm_area_struct * vma)137 bool vma_is_secretmem(struct vm_area_struct *vma)
138 {
139 return vma->vm_ops == &secretmem_vm_ops;
140 }
141
142 static const struct file_operations secretmem_fops = {
143 .release = secretmem_release,
144 .mmap = secretmem_mmap,
145 };
146
secretmem_migrate_folio(struct address_space * mapping,struct folio * dst,struct folio * src,enum migrate_mode mode)147 static int secretmem_migrate_folio(struct address_space *mapping,
148 struct folio *dst, struct folio *src, enum migrate_mode mode)
149 {
150 return -EBUSY;
151 }
152
secretmem_free_folio(struct folio * folio)153 static void secretmem_free_folio(struct folio *folio)
154 {
155 set_direct_map_default_noflush(&folio->page);
156 folio_zero_segment(folio, 0, folio_size(folio));
157 }
158
159 const struct address_space_operations secretmem_aops = {
160 .dirty_folio = noop_dirty_folio,
161 .free_folio = secretmem_free_folio,
162 .migrate_folio = secretmem_migrate_folio,
163 };
164
secretmem_setattr(struct user_namespace * mnt_userns,struct dentry * dentry,struct iattr * iattr)165 static int secretmem_setattr(struct user_namespace *mnt_userns,
166 struct dentry *dentry, struct iattr *iattr)
167 {
168 struct inode *inode = d_inode(dentry);
169 struct address_space *mapping = inode->i_mapping;
170 unsigned int ia_valid = iattr->ia_valid;
171 int ret;
172
173 filemap_invalidate_lock(mapping);
174
175 if ((ia_valid & ATTR_SIZE) && inode->i_size)
176 ret = -EINVAL;
177 else
178 ret = simple_setattr(mnt_userns, dentry, iattr);
179
180 filemap_invalidate_unlock(mapping);
181
182 return ret;
183 }
184
185 static const struct inode_operations secretmem_iops = {
186 .setattr = secretmem_setattr,
187 };
188
189 static struct vfsmount *secretmem_mnt;
190
secretmem_file_create(unsigned long flags)191 static struct file *secretmem_file_create(unsigned long flags)
192 {
193 struct file *file = ERR_PTR(-ENOMEM);
194 struct inode *inode;
195 const char *anon_name = "[secretmem]";
196 const struct qstr qname = QSTR_INIT(anon_name, strlen(anon_name));
197 int err;
198
199 inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
200 if (IS_ERR(inode))
201 return ERR_CAST(inode);
202
203 err = security_inode_init_security_anon(inode, &qname, NULL);
204 if (err) {
205 file = ERR_PTR(err);
206 goto err_free_inode;
207 }
208
209 file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
210 O_RDWR, &secretmem_fops);
211 if (IS_ERR(file))
212 goto err_free_inode;
213
214 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
215 mapping_set_unevictable(inode->i_mapping);
216
217 inode->i_op = &secretmem_iops;
218 inode->i_mapping->a_ops = &secretmem_aops;
219
220 /* pretend we are a normal file with zero size */
221 inode->i_mode |= S_IFREG;
222 inode->i_size = 0;
223
224 return file;
225
226 err_free_inode:
227 iput(inode);
228 return file;
229 }
230
SYSCALL_DEFINE1(memfd_secret,unsigned int,flags)231 SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
232 {
233 struct file *file;
234 int fd, err;
235
236 /* make sure local flags do not confict with global fcntl.h */
237 BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
238
239 if (!secretmem_enable)
240 return -ENOSYS;
241
242 if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
243 return -EINVAL;
244 if (atomic_read(&secretmem_users) < 0)
245 return -ENFILE;
246
247 fd = get_unused_fd_flags(flags & O_CLOEXEC);
248 if (fd < 0)
249 return fd;
250
251 file = secretmem_file_create(flags);
252 if (IS_ERR(file)) {
253 err = PTR_ERR(file);
254 goto err_put_fd;
255 }
256
257 file->f_flags |= O_LARGEFILE;
258
259 atomic_inc(&secretmem_users);
260 fd_install(fd, file);
261 return fd;
262
263 err_put_fd:
264 put_unused_fd(fd);
265 return err;
266 }
267
secretmem_init_fs_context(struct fs_context * fc)268 static int secretmem_init_fs_context(struct fs_context *fc)
269 {
270 return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
271 }
272
273 static struct file_system_type secretmem_fs = {
274 .name = "secretmem",
275 .init_fs_context = secretmem_init_fs_context,
276 .kill_sb = kill_anon_super,
277 };
278
secretmem_init(void)279 static int __init secretmem_init(void)
280 {
281 if (!secretmem_enable)
282 return 0;
283
284 secretmem_mnt = kern_mount(&secretmem_fs);
285 if (IS_ERR(secretmem_mnt))
286 return PTR_ERR(secretmem_mnt);
287
288 /* prevent secretmem mappings from ever getting PROT_EXEC */
289 secretmem_mnt->mnt_flags |= MNT_NOEXEC;
290
291 return 0;
292 }
293 fs_initcall(secretmem_init);
294
