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
38static bool secretmem_enable __ro_after_init = 1;
39module_param_named(enable, secretmem_enable, bool, 0400);
40MODULE_PARM_DESC(secretmem_enable,
41 "Enable secretmem and memfd_secret(2) system call");
42
43static atomic_t secretmem_users;
44
45bool secretmem_active(void)
46{
47 return !!atomic_read(v: &secretmem_users);
48}
49
50static 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(f: 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(err: -EINVAL);
64
65 filemap_invalidate_lock_shared(mapping);
66
67retry:
68 page = find_lock_page(mapping, index: 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, index: 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(start: addr, end: addr + PAGE_SIZE);
103 }
104
105 vmf->page = page;
106 ret = VM_FAULT_LOCKED;
107
108out:
109 filemap_invalidate_unlock_shared(mapping);
110 return ret;
111}
112
113static const struct vm_operations_struct secretmem_vm_ops = {
114 .fault = secretmem_fault,
115};
116
117static int secretmem_release(struct inode *inode, struct file *file)
118{
119 atomic_dec(v: &secretmem_users);
120 return 0;
121}
122
123static int secretmem_mmap_prepare(struct vm_area_desc *desc)
124{
125 const unsigned long len = desc->end - desc->start;
126
127 if ((desc->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
128 return -EINVAL;
129
130 if (!mlock_future_ok(mm: desc->mm, flags: desc->vm_flags | VM_LOCKED, bytes: len))
131 return -EAGAIN;
132
133 desc->vm_flags |= VM_LOCKED | VM_DONTDUMP;
134 desc->vm_ops = &secretmem_vm_ops;
135
136 return 0;
137}
138
139bool vma_is_secretmem(struct vm_area_struct *vma)
140{
141 return vma->vm_ops == &secretmem_vm_ops;
142}
143
144static const struct file_operations secretmem_fops = {
145 .release = secretmem_release,
146 .mmap_prepare = secretmem_mmap_prepare,
147};
148
149static 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
155static void secretmem_free_folio(struct folio *folio)
156{
157 set_direct_map_default_noflush(&folio->page);
158 folio_zero_segment(folio, start: 0, xend: folio_size(folio));
159}
160
161const 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
167static 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
187static const struct inode_operations secretmem_iops = {
188 .setattr = secretmem_setattr,
189};
190
191static struct vfsmount *secretmem_mnt;
192
193static struct file *secretmem_file_create(unsigned long flags)
194{
195 struct file *file;
196 struct inode *inode;
197 const char *anon_name = "[secretmem]";
198 int err;
199
200 inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
201 if (IS_ERR(ptr: inode))
202 return ERR_CAST(ptr: inode);
203
204 err = security_inode_init_security_anon(inode, name: &QSTR(anon_name), NULL);
205 if (err) {
206 file = ERR_PTR(error: err);
207 goto err_free_inode;
208 }
209
210 file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
211 O_RDWR, &secretmem_fops);
212 if (IS_ERR(ptr: file))
213 goto err_free_inode;
214
215 mapping_set_gfp_mask(m: inode->i_mapping, GFP_HIGHUSER);
216 mapping_set_unevictable(mapping: inode->i_mapping);
217
218 inode->i_op = &secretmem_iops;
219 inode->i_mapping->a_ops = &secretmem_aops;
220
221 /* pretend we are a normal file with zero size */
222 inode->i_mode |= S_IFREG;
223 inode->i_size = 0;
224
225 return file;
226
227err_free_inode:
228 iput(inode);
229 return file;
230}
231
232SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
233{
234 struct file *file;
235 int fd, err;
236
237 /* make sure local flags do not confict with global fcntl.h */
238 BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
239
240 if (!secretmem_enable || !can_set_direct_map())
241 return -ENOSYS;
242
243 if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
244 return -EINVAL;
245 if (atomic_read(v: &secretmem_users) < 0)
246 return -ENFILE;
247
248 fd = get_unused_fd_flags(flags: flags & O_CLOEXEC);
249 if (fd < 0)
250 return fd;
251
252 file = secretmem_file_create(flags);
253 if (IS_ERR(ptr: file)) {
254 err = PTR_ERR(ptr: file);
255 goto err_put_fd;
256 }
257
258 file->f_flags |= O_LARGEFILE;
259
260 atomic_inc(v: &secretmem_users);
261 fd_install(fd, file);
262 return fd;
263
264err_put_fd:
265 put_unused_fd(fd);
266 return err;
267}
268
269static int secretmem_init_fs_context(struct fs_context *fc)
270{
271 return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
272}
273
274static struct file_system_type secretmem_fs = {
275 .name = "secretmem",
276 .init_fs_context = secretmem_init_fs_context,
277 .kill_sb = kill_anon_super,
278};
279
280static int __init secretmem_init(void)
281{
282 if (!secretmem_enable || !can_set_direct_map())
283 return 0;
284
285 secretmem_mnt = kern_mount(&secretmem_fs);
286 if (IS_ERR(ptr: secretmem_mnt))
287 return PTR_ERR(ptr: secretmem_mnt);
288
289 /* prevent secretmem mappings from ever getting PROT_EXEC */
290 secretmem_mnt->mnt_flags |= MNT_NOEXEC;
291
292 return 0;
293}
294fs_initcall(secretmem_init);
295

source code of linux/mm/secretmem.c