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 #include <linux/sched/user.h>
22 #include <linux/cred.h>
23
24 #include <uapi/linux/magic.h>
25
26 #include <asm/tlbflush.h>
27
28 #include "internal.h"
29
30 #undef pr_fmt
31 #define pr_fmt(fmt) "secretmem: " fmt
32
33 /*
34 * Define mode and flag masks to allow validation of the system call
35 * parameters.
36 */
37 #define SECRETMEM_MODE_MASK (0x0)
38 #define SECRETMEM_FLAGS_MASK SECRETMEM_MODE_MASK
39
40 static bool secretmem_enable __ro_after_init = 1;
41 module_param_named(enable, secretmem_enable, bool, 0400);
42 MODULE_PARM_DESC(secretmem_enable,
43 "Enable secretmem and memfd_secret(2) system call");
44
45 static atomic_t secretmem_users;
46
secretmem_active(void)47 bool secretmem_active(void)
48 {
49 return !!atomic_read(&secretmem_users);
50 }
51
52 struct secretmem_inode_state {
53 struct user_struct *user;
54 atomic_long_t nr_pages_accounted;
55 };
56
__secretmem_account_pages(struct user_struct * user,unsigned long nr_pages)57 static bool __secretmem_account_pages(struct user_struct *user,
58 unsigned long nr_pages)
59 {
60 unsigned long page_limit, cur_pages, new_pages;
61
62 if (!nr_pages)
63 return true;
64
65 page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
66
67 cur_pages = atomic_long_read(&user->locked_vm);
68 do {
69 new_pages = cur_pages + nr_pages;
70 if (new_pages > page_limit)
71 return false;
72 } while (!atomic_long_try_cmpxchg(&user->locked_vm,
73 &cur_pages, new_pages));
74 return true;
75 }
76
secretmem_account_folio(struct secretmem_inode_state * state,const struct folio * folio)77 static bool secretmem_account_folio(struct secretmem_inode_state *state,
78 const struct folio *folio)
79 {
80 const unsigned long nr_pages = folio_nr_pages(folio);
81
82 if (!__secretmem_account_pages(state->user, nr_pages))
83 return false;
84
85 atomic_long_add(nr_pages, &state->nr_pages_accounted);
86 return true;
87 }
88
__secretmem_unaccount_pages(struct secretmem_inode_state * state,unsigned long nr_pages)89 static void __secretmem_unaccount_pages(struct secretmem_inode_state *state,
90 unsigned long nr_pages)
91 {
92 atomic_long_sub(nr_pages, &state->user->locked_vm);
93 atomic_long_sub(nr_pages, &state->nr_pages_accounted);
94 }
95
secretmem_unaccount_folio(struct secretmem_inode_state * state,struct folio * folio)96 static void secretmem_unaccount_folio(struct secretmem_inode_state *state,
97 struct folio *folio)
98 {
99 __secretmem_unaccount_pages(state, folio_nr_pages(folio));
100 }
101
secretmem_unaccount_all_folios(struct secretmem_inode_state * state)102 static void secretmem_unaccount_all_folios(struct secretmem_inode_state *state)
103 {
104 const unsigned long nr_pages_accounted =
105 atomic_long_read(&state->nr_pages_accounted);
106
107 __secretmem_unaccount_pages(state, nr_pages_accounted);
108 }
109
secretmem_fault(struct vm_fault * vmf)110 static vm_fault_t secretmem_fault(struct vm_fault *vmf)
111 {
112 struct address_space *mapping = vmf->vma->vm_file->f_mapping;
113 struct inode *inode = file_inode(vmf->vma->vm_file);
114 struct secretmem_inode_state *state = inode->i_private;
115 pgoff_t offset = vmf->pgoff;
116 gfp_t gfp = vmf->gfp_mask;
117 unsigned long addr;
118 struct folio *folio;
119 vm_fault_t ret;
120 int err;
121
122 if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
123 return vmf_error(-EINVAL);
124
125 filemap_invalidate_lock_shared(mapping);
126
127 retry:
128 folio = filemap_lock_folio(mapping, offset);
129 if (IS_ERR(folio)) {
130 folio = folio_alloc(gfp | __GFP_ZERO, 0);
131 if (!folio) {
132 ret = VM_FAULT_OOM;
133 goto out;
134 }
135
136 if (!secretmem_account_folio(state, folio)) {
137 folio_put(folio);
138 ret = VM_FAULT_SIGBUS;
139 goto out;
140 }
141
142 err = set_direct_map_invalid_noflush(folio_page(folio, 0));
143 if (err) {
144 secretmem_unaccount_folio(state, folio);
145 folio_put(folio);
146 ret = vmf_error(err);
147 goto out;
148 }
149
150 __folio_mark_uptodate(folio);
151 err = filemap_add_folio(mapping, folio, offset, gfp);
152 if (unlikely(err)) {
153 secretmem_unaccount_folio(state, folio);
154 /*
155 * If a split of large page was required, it
156 * already happened when we marked the page invalid
157 * which guarantees that this call won't fail
158 */
159 set_direct_map_default_noflush(folio_page(folio, 0));
160 folio_put(folio);
161 if (err == -EEXIST)
162 goto retry;
163
164 ret = vmf_error(err);
165 goto out;
166 }
167
168 addr = (unsigned long)folio_address(folio);
169 flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
170 }
171
172 vmf->page = folio_file_page(folio, vmf->pgoff);
173 ret = VM_FAULT_LOCKED;
174
175 out:
176 filemap_invalidate_unlock_shared(mapping);
177 return ret;
178 }
179
180 static const struct vm_operations_struct secretmem_vm_ops = {
181 .fault = secretmem_fault,
182 };
183
secretmem_destroy_inode_priv(struct inode * inode)184 static void secretmem_destroy_inode_priv(struct inode *inode)
185 {
186 struct secretmem_inode_state *state = inode->i_private;
187
188 secretmem_unaccount_all_folios(state);
189 free_uid(state->user);
190 kfree(state);
191 inode->i_private = NULL;
192 }
193
secretmem_release(struct inode * inode,struct file * file)194 static int secretmem_release(struct inode *inode, struct file *file)
195 {
196 atomic_dec(&secretmem_users);
197 secretmem_destroy_inode_priv(inode);
198
199 return 0;
200 }
201
secretmem_mmap_prepare(struct vm_area_desc * desc)202 static int secretmem_mmap_prepare(struct vm_area_desc *desc)
203 {
204 if (!vma_desc_test_any(desc, VMA_SHARED_BIT, VMA_MAYSHARE_BIT))
205 return -EINVAL;
206
207 vma_desc_set_flags(desc, VMA_DONTDUMP_BIT);
208 desc->vm_ops = &secretmem_vm_ops;
209
210 return 0;
211 }
212
vma_is_secretmem(struct vm_area_struct * vma)213 bool vma_is_secretmem(struct vm_area_struct *vma)
214 {
215 return vma->vm_ops == &secretmem_vm_ops;
216 }
217
218 static const struct file_operations secretmem_fops = {
219 .release = secretmem_release,
220 .mmap_prepare = secretmem_mmap_prepare,
221 };
222
secretmem_migrate_folio(struct address_space * mapping,struct folio * dst,struct folio * src,enum migrate_mode mode)223 static int secretmem_migrate_folio(struct address_space *mapping,
224 struct folio *dst, struct folio *src, enum migrate_mode mode)
225 {
226 return -EBUSY;
227 }
228
secretmem_free_folio(struct folio * folio)229 static void secretmem_free_folio(struct folio *folio)
230 {
231 set_direct_map_default_noflush(folio_page(folio, 0));
232 folio_zero_segment(folio, 0, folio_size(folio));
233 }
234
235 const struct address_space_operations secretmem_aops = {
236 .dirty_folio = noop_dirty_folio,
237 .free_folio = secretmem_free_folio,
238 .migrate_folio = secretmem_migrate_folio,
239 };
240
secretmem_setattr(struct mnt_idmap * idmap,struct dentry * dentry,struct iattr * iattr)241 static int secretmem_setattr(struct mnt_idmap *idmap,
242 struct dentry *dentry, struct iattr *iattr)
243 {
244 struct inode *inode = d_inode(dentry);
245 struct address_space *mapping = inode->i_mapping;
246 unsigned int ia_valid = iattr->ia_valid;
247 int ret;
248
249 filemap_invalidate_lock(mapping);
250
251 if ((ia_valid & ATTR_SIZE) && inode->i_size)
252 ret = -EINVAL;
253 else
254 ret = simple_setattr(idmap, dentry, iattr);
255
256 filemap_invalidate_unlock(mapping);
257
258 return ret;
259 }
260
261 static const struct inode_operations secretmem_iops = {
262 .setattr = secretmem_setattr,
263 };
264
265 static struct vfsmount *secretmem_mnt;
266
secretmem_init_inode_priv(struct inode * inode)267 static int secretmem_init_inode_priv(struct inode *inode)
268 {
269 struct secretmem_inode_state *state;
270
271 state = kzalloc_obj(*state);
272 if (!state)
273 return -ENOMEM;
274
275 state->user = get_uid(current_user());
276 inode->i_private = state;
277 return 0;
278 }
279
secretmem_file_create(unsigned long flags)280 static struct file *secretmem_file_create(unsigned long flags)
281 {
282 struct file *file;
283 struct inode *inode;
284 const char *anon_name = "[secretmem]";
285 int err;
286
287 inode = anon_inode_make_secure_inode(secretmem_mnt->mnt_sb, anon_name, NULL);
288 if (IS_ERR(inode))
289 return ERR_CAST(inode);
290
291 err = secretmem_init_inode_priv(inode);
292 if (err)
293 goto err_free_inode;
294
295 file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
296 O_RDWR | O_LARGEFILE, &secretmem_fops);
297 if (IS_ERR(file)) {
298 err = PTR_ERR(file);
299 goto err_free_priv;
300 }
301
302 mapping_set_gfp_mask(inode->i_mapping, GFP_USER);
303 mapping_set_unevictable(inode->i_mapping);
304
305 inode->i_op = &secretmem_iops;
306 inode->i_mapping->a_ops = &secretmem_aops;
307
308 /* pretend we are a normal file with zero size */
309 inode->i_mode |= S_IFREG;
310 inode->i_size = 0;
311
312 atomic_inc(&secretmem_users);
313
314 return file;
315 err_free_priv:
316 secretmem_destroy_inode_priv(inode);
317 err_free_inode:
318 iput(inode);
319 return ERR_PTR(err);
320 }
321
SYSCALL_DEFINE1(memfd_secret,unsigned int,flags)322 SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
323 {
324 /* make sure local flags do not conflict with global fcntl.h */
325 BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
326
327 if (!secretmem_enable || !can_set_direct_map())
328 return -ENOSYS;
329
330 if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
331 return -EINVAL;
332 if (atomic_read(&secretmem_users) < 0)
333 return -ENFILE;
334
335 return FD_ADD(flags & O_CLOEXEC, secretmem_file_create(flags));
336 }
337
secretmem_init_fs_context(struct fs_context * fc)338 static int secretmem_init_fs_context(struct fs_context *fc)
339 {
340 struct pseudo_fs_context *ctx;
341
342 ctx = init_pseudo(fc, SECRETMEM_MAGIC);
343 if (!ctx)
344 return -ENOMEM;
345
346 return 0;
347 }
348
349 static struct file_system_type secretmem_fs = {
350 .name = "secretmem",
351 .init_fs_context = secretmem_init_fs_context,
352 .kill_sb = kill_anon_super,
353 };
354
secretmem_init(void)355 static int __init secretmem_init(void)
356 {
357 if (!secretmem_enable || !can_set_direct_map())
358 return 0;
359
360 secretmem_mnt = kern_mount(&secretmem_fs);
361 if (IS_ERR(secretmem_mnt))
362 return PTR_ERR(secretmem_mnt);
363
364 return 0;
365 }
366 fs_initcall(secretmem_init);
367