mm/secretmem.c

   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
  45 bool secretmem_active(void)
  46 {
  47         return !!atomic_read(&secretmem_users);
  48 }
  49
  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         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
  66 retry:
  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
 106 out:
 107         filemap_invalidate_unlock_shared(mapping);
 108         return ret;
 109 }
 110
 111 static const struct vm_operations_struct secretmem_vm_ops = {
 112         .fault = secretmem_fault,
 113 };
 114
 115 static int secretmem_release(struct inode *inode, struct file *file)
 116 {
 117         atomic_dec(&secretmem_users);
 118         return 0;
 119 }
 120
 121 static 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         vm_flags_set(vma, VM_LOCKED | VM_DONTDUMP);
 132         vma->vm_ops = &secretmem_vm_ops;
 133
 134         return 0;
 135 }
 136
 137 bool vma_is_secretmem(struct vm_area_struct *vma)
 138 {
 139         return vma->vm_ops == &secretmem_vm_ops;
 140 }
 141
 142 static const struct file_operations secretmem_fops = {
 143         .release        = secretmem_release,
 144         .mmap           = secretmem_mmap,
 145 };
 146
 147 static 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
 153 static 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
 159 const 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
 165 static int secretmem_setattr(struct mnt_idmap *idmap,
 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(idmap, dentry, iattr);
 179
 180         filemap_invalidate_unlock(mapping);
 181
 182         return ret;
 183 }
 184
 185 static const struct inode_operations secretmem_iops = {
 186         .setattr = secretmem_setattr,
 187 };
 188
 189 static struct vfsmount *secretmem_mnt;
 190
 191 static struct file *secretmem_file_create(unsigned long flags)
 192 {
 193         struct file *file;
 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
 226 err_free_inode:
 227         iput(inode);
 228         return file;
 229 }
 230
 231 SYSCALL_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
 263 err_put_fd:
 264         put_unused_fd(fd);
 265         return err;
 266 }
 267
 268 static int secretmem_init_fs_context(struct fs_context *fc)
 269 {
 270         return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
 271 }
 272
 273 static 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
 279 static 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 }
 293 fs_initcall(secretmem_init);