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1// SPDX-License-Identifier: GPL-2.02/*3 * fs/ext4/verity.c: fs-verity support for ext44 *5 * Copyright 2019 Google LLC6 */7 8/*9 * Implementation of fsverity_operations for ext4.10 *11 * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past12 * the end of the file, starting at the first 64K boundary beyond i_size. This13 * approach works because (a) verity files are readonly, and (b) pages fully14 * beyond i_size aren't visible to userspace but can be read/written internally15 * by ext4 with only some relatively small changes to ext4. This approach16 * avoids having to depend on the EA_INODE feature and on rearchitecturing17 * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and18 * to support encrypting xattrs. Note that the verity metadata *must* be19 * encrypted when the file is, since it contains hashes of the plaintext data.20 *21 * Using a 64K boundary rather than a 4K one keeps things ready for22 * architectures with 64K pages, and it doesn't necessarily waste space on-disk23 * since there can be a hole between i_size and the start of the Merkle tree.24 */25 26#include <linux/quotaops.h>27 28#include "ext4.h"29#include "ext4_extents.h"30#include "ext4_jbd2.h"31 32static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)33{34 return round_up(inode->i_size, 65536);35}36 37/*38 * Read some verity metadata from the inode. __vfs_read() can't be used because39 * we need to read beyond i_size.40 */41static int pagecache_read(struct inode *inode, void *buf, size_t count,42 loff_t pos)43{44 while (count) {45 struct folio *folio;46 size_t n;47 48 folio = read_mapping_folio(inode->i_mapping, pos >> PAGE_SHIFT,49 NULL);50 if (IS_ERR(folio))51 return PTR_ERR(folio);52 53 n = memcpy_from_file_folio(buf, folio, pos, count);54 folio_put(folio);55 56 buf += n;57 pos += n;58 count -= n;59 }60 return 0;61}62 63/*64 * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.65 * kernel_write() can't be used because the file descriptor is readonly.66 */67static int pagecache_write(struct inode *inode, const void *buf, size_t count,68 loff_t pos)69{70 struct address_space *mapping = inode->i_mapping;71 const struct address_space_operations *aops = mapping->a_ops;72 73 if (pos + count > inode->i_sb->s_maxbytes)74 return -EFBIG;75 76 while (count) {77 size_t n = min_t(size_t, count,78 PAGE_SIZE - offset_in_page(pos));79 struct folio *folio;80 void *fsdata = NULL;81 int res;82 83 res = aops->write_begin(NULL, mapping, pos, n, &folio, &fsdata);84 if (res)85 return res;86 87 memcpy_to_folio(folio, offset_in_folio(folio, pos), buf, n);88 89 res = aops->write_end(NULL, mapping, pos, n, n, folio, fsdata);90 if (res < 0)91 return res;92 if (res != n)93 return -EIO;94 95 buf += n;96 pos += n;97 count -= n;98 }99 return 0;100}101 102static int ext4_begin_enable_verity(struct file *filp)103{104 struct inode *inode = file_inode(filp);105 const int credits = 2; /* superblock and inode for ext4_orphan_add() */106 handle_t *handle;107 int err;108 109 if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX))110 return -EINVAL;111 112 if (ext4_verity_in_progress(inode))113 return -EBUSY;114 115 /*116 * Since the file was opened readonly, we have to initialize the jbd117 * inode and quotas here and not rely on ->open() doing it. This must118 * be done before evicting the inline data.119 */120 121 err = ext4_inode_attach_jinode(inode);122 if (err)123 return err;124 125 err = dquot_initialize(inode);126 if (err)127 return err;128 129 err = ext4_convert_inline_data(inode);130 if (err)131 return err;132 133 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {134 ext4_warning_inode(inode,135 "verity is only allowed on extent-based files");136 return -EOPNOTSUPP;137 }138 139 /*140 * ext4 uses the last allocated block to find the verity descriptor, so141 * we must remove any other blocks past EOF which might confuse things.142 */143 err = ext4_truncate(inode);144 if (err)145 return err;146 147 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);148 if (IS_ERR(handle))149 return PTR_ERR(handle);150 151 err = ext4_orphan_add(handle, inode);152 if (err == 0)153 ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);154 155 ext4_journal_stop(handle);156 return err;157}158 159/*160 * ext4 stores the verity descriptor beginning on the next filesystem block161 * boundary after the Merkle tree. Then, the descriptor size is stored in the162 * last 4 bytes of the last allocated filesystem block --- which is either the163 * block in which the descriptor ends, or the next block after that if there164 * weren't at least 4 bytes remaining.165 *166 * We can't simply store the descriptor in an xattr because it *must* be167 * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt168 * xattrs. Also, if the descriptor includes a large signature blob it may be169 * too large to store in an xattr without the EA_INODE feature.170 */171static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,172 size_t desc_size, u64 merkle_tree_size)173{174 const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +175 merkle_tree_size, i_blocksize(inode));176 const u64 desc_end = desc_pos + desc_size;177 const __le32 desc_size_disk = cpu_to_le32(desc_size);178 const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),179 i_blocksize(inode)) -180 sizeof(desc_size_disk);181 int err;182 183 err = pagecache_write(inode, desc, desc_size, desc_pos);184 if (err)185 return err;186 187 return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),188 desc_size_pos);189}190 191static int ext4_end_enable_verity(struct file *filp, const void *desc,192 size_t desc_size, u64 merkle_tree_size)193{194 struct inode *inode = file_inode(filp);195 const int credits = 2; /* superblock and inode for ext4_orphan_del() */196 handle_t *handle;197 struct ext4_iloc iloc;198 int err = 0;199 200 /*201 * If an error already occurred (which fs/verity/ signals by passing202 * desc == NULL), then only clean-up is needed.203 */204 if (desc == NULL)205 goto cleanup;206 207 /* Append the verity descriptor. */208 err = ext4_write_verity_descriptor(inode, desc, desc_size,209 merkle_tree_size);210 if (err)211 goto cleanup;212 213 /*214 * Write all pages (both data and verity metadata). Note that this must215 * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages216 * beyond i_size won't be written properly. For crash consistency, this217 * also must happen before the verity inode flag gets persisted.218 */219 err = filemap_write_and_wait(inode->i_mapping);220 if (err)221 goto cleanup;222 223 /*224 * Finally, set the verity inode flag and remove the inode from the225 * orphan list (in a single transaction).226 */227 228 handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);229 if (IS_ERR(handle)) {230 err = PTR_ERR(handle);231 goto cleanup;232 }233 234 err = ext4_orphan_del(handle, inode);235 if (err)236 goto stop_and_cleanup;237 238 err = ext4_reserve_inode_write(handle, inode, &iloc);239 if (err)240 goto stop_and_cleanup;241 242 ext4_set_inode_flag(inode, EXT4_INODE_VERITY);243 ext4_set_inode_flags(inode, false);244 err = ext4_mark_iloc_dirty(handle, inode, &iloc);245 if (err)246 goto stop_and_cleanup;247 248 ext4_journal_stop(handle);249 250 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);251 return 0;252 253stop_and_cleanup:254 ext4_journal_stop(handle);255cleanup:256 /*257 * Verity failed to be enabled, so clean up by truncating any verity258 * metadata that was written beyond i_size (both from cache and from259 * disk), removing the inode from the orphan list (if it wasn't done260 * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS.261 */262 truncate_inode_pages(inode->i_mapping, inode->i_size);263 ext4_truncate(inode);264 ext4_orphan_del(NULL, inode);265 ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);266 return err;267}268 269static int ext4_get_verity_descriptor_location(struct inode *inode,270 size_t *desc_size_ret,271 u64 *desc_pos_ret)272{273 struct ext4_ext_path *path;274 struct ext4_extent *last_extent;275 u32 end_lblk;276 u64 desc_size_pos;277 __le32 desc_size_disk;278 u32 desc_size;279 u64 desc_pos;280 int err;281 282 /*283 * Descriptor size is in last 4 bytes of last allocated block.284 * See ext4_write_verity_descriptor().285 */286 287 if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {288 EXT4_ERROR_INODE(inode, "verity file doesn't use extents");289 return -EFSCORRUPTED;290 }291 292 path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);293 if (IS_ERR(path))294 return PTR_ERR(path);295 296 last_extent = path[path->p_depth].p_ext;297 if (!last_extent) {298 EXT4_ERROR_INODE(inode, "verity file has no extents");299 ext4_free_ext_path(path);300 return -EFSCORRUPTED;301 }302 303 end_lblk = le32_to_cpu(last_extent->ee_block) +304 ext4_ext_get_actual_len(last_extent);305 desc_size_pos = (u64)end_lblk << inode->i_blkbits;306 ext4_free_ext_path(path);307 308 if (desc_size_pos < sizeof(desc_size_disk))309 goto bad;310 desc_size_pos -= sizeof(desc_size_disk);311 312 err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),313 desc_size_pos);314 if (err)315 return err;316 desc_size = le32_to_cpu(desc_size_disk);317 318 /*319 * The descriptor is stored just before the desc_size_disk, but starting320 * on a filesystem block boundary.321 */322 323 if (desc_size > INT_MAX || desc_size > desc_size_pos)324 goto bad;325 326 desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));327 if (desc_pos < ext4_verity_metadata_pos(inode))328 goto bad;329 330 *desc_size_ret = desc_size;331 *desc_pos_ret = desc_pos;332 return 0;333 334bad:335 EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");336 return -EFSCORRUPTED;337}338 339static int ext4_get_verity_descriptor(struct inode *inode, void *buf,340 size_t buf_size)341{342 size_t desc_size = 0;343 u64 desc_pos = 0;344 int err;345 346 err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);347 if (err)348 return err;349 350 if (buf_size) {351 if (desc_size > buf_size)352 return -ERANGE;353 err = pagecache_read(inode, buf, desc_size, desc_pos);354 if (err)355 return err;356 }357 return desc_size;358}359 360static struct page *ext4_read_merkle_tree_page(struct inode *inode,361 pgoff_t index,362 unsigned long num_ra_pages)363{364 struct folio *folio;365 366 index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;367 368 folio = __filemap_get_folio(inode->i_mapping, index, FGP_ACCESSED, 0);369 if (IS_ERR(folio) || !folio_test_uptodate(folio)) {370 DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index);371 372 if (!IS_ERR(folio))373 folio_put(folio);374 else if (num_ra_pages > 1)375 page_cache_ra_unbounded(&ractl, num_ra_pages, 0);376 folio = read_mapping_folio(inode->i_mapping, index, NULL);377 if (IS_ERR(folio))378 return ERR_CAST(folio);379 }380 return folio_file_page(folio, index);381}382 383static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,384 u64 pos, unsigned int size)385{386 pos += ext4_verity_metadata_pos(inode);387 388 return pagecache_write(inode, buf, size, pos);389}390 391const struct fsverity_operations ext4_verityops = {392 .begin_enable_verity = ext4_begin_enable_verity,393 .end_enable_verity = ext4_end_enable_verity,394 .get_verity_descriptor = ext4_get_verity_descriptor,395 .read_merkle_tree_page = ext4_read_merkle_tree_page,396 .write_merkle_tree_block = ext4_write_merkle_tree_block,397};398