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
38 static bool secretmem_enable __ro_after_init;
39 module_param_named(enable, secretmem_enable, bool, 0400);
40 MODULE_PARM_DESC(secretmem_enable,
41 "Enable secretmem and memfd_secret(2) system call");
42
43 static atomic_t secretmem_users;
44
secretmem_active(void)45 bool secretmem_active(void)
46 {
47 return !!atomic_read(&secretmem_users);
48 }
49
secretmem_fault(struct vm_fault * vmf)50 static 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
63 retry:
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
100 static const struct vm_operations_struct secretmem_vm_ops = {
101 .fault = secretmem_fault,
102 };
103
secretmem_release(struct inode * inode,struct file * file)104 static int secretmem_release(struct inode *inode, struct file *file)
105 {
106 atomic_dec(&secretmem_users);
107 return 0;
108 }
109
secretmem_mmap(struct file * file,struct vm_area_struct * vma)110 static 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
vma_is_secretmem(struct vm_area_struct * vma)126 bool vma_is_secretmem(struct vm_area_struct *vma)
127 {
128 return vma->vm_ops == &secretmem_vm_ops;
129 }
130
131 static const struct file_operations secretmem_fops = {
132 .release = secretmem_release,
133 .mmap = secretmem_mmap,
134 };
135
secretmem_isolate_page(struct page * page,isolate_mode_t mode)136 static bool secretmem_isolate_page(struct page *page, isolate_mode_t mode)
137 {
138 return false;
139 }
140
secretmem_migratepage(struct address_space * mapping,struct page * newpage,struct page * page,enum migrate_mode mode)141 static 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
secretmem_freepage(struct page * page)148 static void secretmem_freepage(struct page *page)
149 {
150 set_direct_map_default_noflush(page);
151 clear_highpage(page);
152 }
153
154 const 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
161 static struct vfsmount *secretmem_mnt;
162
secretmem_file_create(unsigned long flags)163 static 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
188 err_free_inode:
189 iput(inode);
190 return file;
191 }
192
SYSCALL_DEFINE1(memfd_secret,unsigned int,flags)193 SYSCALL_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 if (atomic_read(&secretmem_users) < 0)
207 return -ENFILE;
208
209 fd = get_unused_fd_flags(flags & O_CLOEXEC);
210 if (fd < 0)
211 return fd;
212
213 file = secretmem_file_create(flags);
214 if (IS_ERR(file)) {
215 err = PTR_ERR(file);
216 goto err_put_fd;
217 }
218
219 file->f_flags |= O_LARGEFILE;
220
221 atomic_inc(&secretmem_users);
222 fd_install(fd, file);
223 return fd;
224
225 err_put_fd:
226 put_unused_fd(fd);
227 return err;
228 }
229
secretmem_init_fs_context(struct fs_context * fc)230 static int secretmem_init_fs_context(struct fs_context *fc)
231 {
232 return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
233 }
234
235 static struct file_system_type secretmem_fs = {
236 .name = "secretmem",
237 .init_fs_context = secretmem_init_fs_context,
238 .kill_sb = kill_anon_super,
239 };
240
secretmem_init(void)241 static int secretmem_init(void)
242 {
243 int ret = 0;
244
245 if (!secretmem_enable)
246 return ret;
247
248 secretmem_mnt = kern_mount(&secretmem_fs);
249 if (IS_ERR(secretmem_mnt))
250 ret = PTR_ERR(secretmem_mnt);
251
252 /* prevent secretmem mappings from ever getting PROT_EXEC */
253 secretmem_mnt->mnt_flags |= MNT_NOEXEC;
254
255 return ret;
256 }
257 fs_initcall(secretmem_init);
258