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;
 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	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
 66retry:
 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
106out:
107	filemap_invalidate_unlock_shared(mapping);
108	return ret;
109}
110
111static const struct vm_operations_struct secretmem_vm_ops = {
112	.fault = secretmem_fault,
113};
114
115static int secretmem_release(struct inode *inode, struct file *file)
116{
117	atomic_dec(&secretmem_users);
118	return 0;
119}
120
121static 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
137bool vma_is_secretmem(struct vm_area_struct *vma)
138{
139	return vma->vm_ops == &secretmem_vm_ops;
140}
141
142static const struct file_operations secretmem_fops = {
143	.release	= secretmem_release,
144	.mmap		= secretmem_mmap,
145};
146
147static 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
153static 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
159const 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
165static 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
185static const struct inode_operations secretmem_iops = {
186	.setattr = secretmem_setattr,
187};
188
189static struct vfsmount *secretmem_mnt;
190
191static 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
226err_free_inode:
227	iput(inode);
228	return file;
229}
230
231SYSCALL_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
263err_put_fd:
264	put_unused_fd(fd);
265	return err;
266}
267
268static int secretmem_init_fs_context(struct fs_context *fc)
269{
270	return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
271}
272
273static 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
279static 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}
293fs_initcall(secretmem_init);