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(&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(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
67retry:
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
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(&secretmem_users);
120	return 0;
121}
122
123static 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
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		= secretmem_mmap,
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, 0, 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	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
228err_free_inode:
229	iput(inode);
230	return file;
231}
232
233SYSCALL_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)
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
265err_put_fd:
266	put_unused_fd(fd);
267	return err;
268}
269
270static int secretmem_init_fs_context(struct fs_context *fc)
271{
272	return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
273}
274
275static 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
281static int __init secretmem_init(void)
282{
283	if (!secretmem_enable)
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}
295fs_initcall(secretmem_init);
296