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 = 1;
  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         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
  67 retry:
  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
 108 out:
 109         filemap_invalidate_unlock_shared(mapping);
 110         return ret;
 111 }
 112
 113 static const struct vm_operations_struct secretmem_vm_ops = {
 114         .fault = secretmem_fault,
 115 };
 116
 117 static int secretmem_release(struct inode *inode, struct file *file)
 118 {
 119         atomic_dec(&secretmem_users);
 120         return 0;
 121 }
 122
 123 static 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
 139 bool vma_is_secretmem(struct vm_area_struct *vma)
 140 {
 141         return vma->vm_ops == &secretmem_vm_ops;
 142 }
 143
 144 static const struct file_operations secretmem_fops = {
 145         .release        = secretmem_release,
 146         .mmap           = secretmem_mmap,
 147 };
 148
 149 static 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
 155 static 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
 161 const 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
 167 static 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
 187 static const struct inode_operations secretmem_iops = {
 188         .setattr = secretmem_setattr,
 189 };
 190
 191 static struct vfsmount *secretmem_mnt;
 192
 193 static 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
 228 err_free_inode:
 229         iput(inode);
 230         return file;
 231 }
 232
 233 SYSCALL_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
 265 err_put_fd:
 266         put_unused_fd(fd);
 267         return err;
 268 }
 269
 270 static int secretmem_init_fs_context(struct fs_context *fc)
 271 {
 272         return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
 273 }
 274
 275 static 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
 281 static 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 }
 295 fs_initcall(secretmem_init);