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	int err;
 59
 60	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
 61		return vmf_error(-EINVAL);
 62
 63retry:
 64	page = find_lock_page(mapping, offset);
 65	if (!page) {
 66		page = alloc_page(gfp | __GFP_ZERO);
 67		if (!page)
 68			return VM_FAULT_OOM;
 69
 70		err = set_direct_map_invalid_noflush(page);
 71		if (err) {
 72			put_page(page);
 73			return vmf_error(err);
 74		}
 75
 76		__SetPageUptodate(page);
 77		err = add_to_page_cache_lru(page, mapping, offset, gfp);
 78		if (unlikely(err)) {
 79			put_page(page);
 80			/*
 81			 * If a split of large page was required, it
 82			 * already happened when we marked the page invalid
 83			 * which guarantees that this call won't fail
 84			 */
 85			set_direct_map_default_noflush(page);
 86			if (err == -EEXIST)
 87				goto retry;
 88
 89			return vmf_error(err);
 90		}
 91
 92		addr = (unsigned long)page_address(page);
 93		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 94	}
 95
 96	vmf->page = page;
 97	return VM_FAULT_LOCKED;
 98}
 99
100static const struct vm_operations_struct secretmem_vm_ops = {
101	.fault = secretmem_fault,
102};
103
104static int secretmem_release(struct inode *inode, struct file *file)
105{
106	atomic_dec(&secretmem_users);
107	return 0;
108}
109
110static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
111{
112	unsigned long len = vma->vm_end - vma->vm_start;
113
114	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
115		return -EINVAL;
116
117	if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
118		return -EAGAIN;
119
120	vma->vm_flags |= VM_LOCKED | VM_DONTDUMP;
121	vma->vm_ops = &secretmem_vm_ops;
122
123	return 0;
124}
125
126bool vma_is_secretmem(struct vm_area_struct *vma)
127{
128	return vma->vm_ops == &secretmem_vm_ops;
129}
130
131static const struct file_operations secretmem_fops = {
132	.release	= secretmem_release,
133	.mmap		= secretmem_mmap,
134};
135
136static bool secretmem_isolate_page(struct page *page, isolate_mode_t mode)
137{
138	return false;
139}
140
141static int secretmem_migratepage(struct address_space *mapping,
142				 struct page *newpage, struct page *page,
143				 enum migrate_mode mode)
144{
145	return -EBUSY;
146}
147
148static void secretmem_freepage(struct page *page)
149{
150	set_direct_map_default_noflush(page);
151	clear_highpage(page);
152}
153
154const struct address_space_operations secretmem_aops = {
155	.set_page_dirty	= __set_page_dirty_no_writeback,
156	.freepage	= secretmem_freepage,
157	.migratepage	= secretmem_migratepage,
158	.isolate_page	= secretmem_isolate_page,
159};
160
161static struct vfsmount *secretmem_mnt;
162
163static struct file *secretmem_file_create(unsigned long flags)
164{
165	struct file *file = ERR_PTR(-ENOMEM);
166	struct inode *inode;
167
168	inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
169	if (IS_ERR(inode))
170		return ERR_CAST(inode);
171
172	file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
173				 O_RDWR, &secretmem_fops);
174	if (IS_ERR(file))
175		goto err_free_inode;
176
177	mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
178	mapping_set_unevictable(inode->i_mapping);
179
180	inode->i_mapping->a_ops = &secretmem_aops;
181
182	/* pretend we are a normal file with zero size */
183	inode->i_mode |= S_IFREG;
184	inode->i_size = 0;
185
186	return file;
187
188err_free_inode:
189	iput(inode);
190	return file;
191}
192
193SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
194{
195	struct file *file;
196	int fd, err;
197
198	/* make sure local flags do not confict with global fcntl.h */
199	BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);
200
201	if (!secretmem_enable)
202		return -ENOSYS;
203
204	if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
205		return -EINVAL;
206
207	fd = get_unused_fd_flags(flags & O_CLOEXEC);
208	if (fd < 0)
209		return fd;
210
211	file = secretmem_file_create(flags);
212	if (IS_ERR(file)) {
213		err = PTR_ERR(file);
214		goto err_put_fd;
215	}
216
217	file->f_flags |= O_LARGEFILE;
218
219	fd_install(fd, file);
220	atomic_inc(&secretmem_users);
221	return fd;
222
223err_put_fd:
224	put_unused_fd(fd);
225	return err;
226}
227
228static int secretmem_init_fs_context(struct fs_context *fc)
229{
230	return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
231}
232
233static struct file_system_type secretmem_fs = {
234	.name		= "secretmem",
235	.init_fs_context = secretmem_init_fs_context,
236	.kill_sb	= kill_anon_super,
237};
238
239static int secretmem_init(void)
240{
241	int ret = 0;
242
243	if (!secretmem_enable)
244		return ret;
245
246	secretmem_mnt = kern_mount(&secretmem_fs);
247	if (IS_ERR(secretmem_mnt))
248		ret = PTR_ERR(secretmem_mnt);
249
250	/* prevent secretmem mappings from ever getting PROT_EXEC */
251	secretmem_mnt->mnt_flags |= MNT_NOEXEC;
252
253	return ret;
254}
255fs_initcall(secretmem_init);