// SPDX-License-Identifier: GPL-2.0 /* * fs/ext4/verity.c: fs-verity support for ext4 * * Copyright 2019 Google LLC */ /* * Implementation of fsverity_operations for ext4. * * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past * the end of the file, starting at the first 64K boundary beyond i_size. This * approach works because (a) verity files are readonly, and (b) pages fully * beyond i_size aren't visible to userspace but can be read/written internally * by ext4 with only some relatively small changes to ext4. This approach * avoids having to depend on the EA_INODE feature and on rearchitecturing * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and * to support encrypting xattrs. Note that the verity metadata *must* be * encrypted when the file is, since it contains hashes of the plaintext data. * * Using a 64K boundary rather than a 4K one keeps things ready for * architectures with 64K pages, and it doesn't necessarily waste space on-disk * since there can be a hole between i_size and the start of the Merkle tree. */ #include <linux/quotaops.h> #include "ext4.h" #include "ext4_extents.h" #include "ext4_jbd2.h" static inline loff_t ext4_verity_metadata_pos(const struct inode *inode) { return round_up(inode->i_size, 65536); } /* * Read some verity metadata from the inode. __vfs_read() can't be used because * we need to read beyond i_size. */ static int pagecache_read(struct inode *inode, void *buf, size_t count, loff_t pos) { while (count) { size_t n = min_t(size_t, count, PAGE_SIZE - offset_in_page(pos)); struct page *page; page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT, NULL); if (IS_ERR(page)) return PTR_ERR(page); memcpy_from_page(buf, page, offset_in_page(pos), n); put_page(page); buf += n; pos += n; count -= n; } return 0; } /* * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY. * kernel_write() can't be used because the file descriptor is readonly. */ static int pagecache_write(struct inode *inode, const void *buf, size_t count, loff_t pos) { if (pos + count > inode->i_sb->s_maxbytes) return -EFBIG; while (count) { size_t n = min_t(size_t, count, PAGE_SIZE - offset_in_page(pos)); struct page *page; void *fsdata; int res; res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0, &page, &fsdata); if (res) return res; memcpy_to_page(page, offset_in_page(pos), buf, n); res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n, page, fsdata); if (res < 0) return res; if (res != n) return -EIO; buf += n; pos += n; count -= n; } return 0; } static int ext4_begin_enable_verity(struct file *filp) { struct inode *inode = file_inode(filp); const int credits = 2; /* superblock and inode for ext4_orphan_add() */ handle_t *handle; int err; if (IS_DAX(inode) || ext4_test_inode_flag(inode, EXT4_INODE_DAX)) return -EINVAL; if (ext4_verity_in_progress(inode)) return -EBUSY; /* * Since the file was opened readonly, we have to initialize the jbd * inode and quotas here and not rely on ->open() doing it. This must * be done before evicting the inline data. */ err = ext4_inode_attach_jinode(inode); if (err) return err; err = dquot_initialize(inode); if (err) return err; err = ext4_convert_inline_data(inode); if (err) return err; if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) { ext4_warning_inode(inode, "verity is only allowed on extent-based files"); return -EOPNOTSUPP; } /* * ext4 uses the last allocated block to find the verity descriptor, so * we must remove any other blocks past EOF which might confuse things. */ err = ext4_truncate(inode); if (err) return err; handle = ext4_journal_start(inode, EXT4_HT_INODE, credits); if (IS_ERR(handle)) return PTR_ERR(handle); err = ext4_orphan_add(handle, inode); if (err == 0) ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS); ext4_journal_stop(handle); return err; } /* * ext4 stores the verity descriptor beginning on the next filesystem block * boundary after the Merkle tree. Then, the descriptor size is stored in the * last 4 bytes of the last allocated filesystem block --- which is either the * block in which the descriptor ends, or the next block after that if there * weren't at least 4 bytes remaining. * * We can't simply store the descriptor in an xattr because it *must* be * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt * xattrs. Also, if the descriptor includes a large signature blob it may be * too large to store in an xattr without the EA_INODE feature. */ static int ext4_write_verity_descriptor(struct inode *inode, const void *desc, size_t desc_size, u64 merkle_tree_size) { const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) + merkle_tree_size, i_blocksize(inode)); const u64 desc_end = desc_pos + desc_size; const __le32 desc_size_disk = cpu_to_le32(desc_size); const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk), i_blocksize(inode)) - sizeof(desc_size_disk); int err; err = pagecache_write(inode, desc, desc_size, desc_pos); if (err) return err; return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk), desc_size_pos); } static int ext4_end_enable_verity(struct file *filp, const void *desc, size_t desc_size, u64 merkle_tree_size) { struct inode *inode = file_inode(filp); const int credits = 2; /* superblock and inode for ext4_orphan_del() */ handle_t *handle; struct ext4_iloc iloc; int err = 0; /* * If an error already occurred (which fs/verity/ signals by passing * desc == NULL), then only clean-up is needed. */ if (desc == NULL) goto cleanup; /* Append the verity descriptor. */ err = ext4_write_verity_descriptor(inode, desc, desc_size, merkle_tree_size); if (err) goto cleanup; /* * Write all pages (both data and verity metadata). Note that this must * happen before clearing EXT4_STATE_VERITY_IN_PROGRESS; otherwise pages * beyond i_size won't be written properly. For crash consistency, this * also must happen before the verity inode flag gets persisted. */ err = filemap_write_and_wait(inode->i_mapping); if (err) goto cleanup; /* * Finally, set the verity inode flag and remove the inode from the * orphan list (in a single transaction). */ handle = ext4_journal_start(inode, EXT4_HT_INODE, credits); if (IS_ERR(handle)) { err = PTR_ERR(handle); goto cleanup; } err = ext4_orphan_del(handle, inode); if (err) goto stop_and_cleanup; err = ext4_reserve_inode_write(handle, inode, &iloc); if (err) goto stop_and_cleanup; ext4_set_inode_flag(inode, EXT4_INODE_VERITY); ext4_set_inode_flags(inode, false); err = ext4_mark_iloc_dirty(handle, inode, &iloc); if (err) goto stop_and_cleanup; ext4_journal_stop(handle); ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS); return 0; stop_and_cleanup: ext4_journal_stop(handle); cleanup: /* * Verity failed to be enabled, so clean up by truncating any verity * metadata that was written beyond i_size (both from cache and from * disk), removing the inode from the orphan list (if it wasn't done * already), and clearing EXT4_STATE_VERITY_IN_PROGRESS. */ truncate_inode_pages(inode->i_mapping, inode->i_size); ext4_truncate(inode); ext4_orphan_del(NULL, inode); ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS); return err; } static int ext4_get_verity_descriptor_location(struct inode *inode, size_t *desc_size_ret, u64 *desc_pos_ret) { struct ext4_ext_path *path; struct ext4_extent *last_extent; u32 end_lblk; u64 desc_size_pos; __le32 desc_size_disk; u32 desc_size; u64 desc_pos; int err; /* * Descriptor size is in last 4 bytes of last allocated block. * See ext4_write_verity_descriptor(). */ if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) { EXT4_ERROR_INODE(inode, "verity file doesn't use extents"); return -EFSCORRUPTED; } path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0); if (IS_ERR(path)) return PTR_ERR(path); last_extent = path[path->p_depth].p_ext; if (!last_extent) { EXT4_ERROR_INODE(inode, "verity file has no extents"); ext4_ext_drop_refs(path); kfree(path); return -EFSCORRUPTED; } end_lblk = le32_to_cpu(last_extent->ee_block) + ext4_ext_get_actual_len(last_extent); desc_size_pos = (u64)end_lblk << inode->i_blkbits; ext4_ext_drop_refs(path); kfree(path); if (desc_size_pos < sizeof(desc_size_disk)) goto bad; desc_size_pos -= sizeof(desc_size_disk); err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk), desc_size_pos); if (err) return err; desc_size = le32_to_cpu(desc_size_disk); /* * The descriptor is stored just before the desc_size_disk, but starting * on a filesystem block boundary. */ if (desc_size > INT_MAX || desc_size > desc_size_pos) goto bad; desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode)); if (desc_pos < ext4_verity_metadata_pos(inode)) goto bad; *desc_size_ret = desc_size; *desc_pos_ret = desc_pos; return 0; bad: EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor"); return -EFSCORRUPTED; } static int ext4_get_verity_descriptor(struct inode *inode, void *buf, size_t buf_size) { size_t desc_size = 0; u64 desc_pos = 0; int err; err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos); if (err) return err; if (buf_size) { if (desc_size > buf_size) return -ERANGE; err = pagecache_read(inode, buf, desc_size, desc_pos); if (err) return err; } return desc_size; } static struct page *ext4_read_merkle_tree_page(struct inode *inode, pgoff_t index, unsigned long num_ra_pages) { DEFINE_READAHEAD(ractl, NULL, NULL, inode->i_mapping, index); struct page *page; index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT; page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED); if (!page || !PageUptodate(page)) { if (page) put_page(page); else if (num_ra_pages > 1) page_cache_ra_unbounded(&ractl, num_ra_pages, 0); page = read_mapping_page(inode->i_mapping, index, NULL); } return page; } static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf, u64 index, int log_blocksize) { loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize); return pagecache_write(inode, buf, 1 << log_blocksize, pos); } const struct fsverity_operations ext4_verityops = { .begin_enable_verity = ext4_begin_enable_verity, .end_enable_verity = ext4_end_enable_verity, .get_verity_descriptor = ext4_get_verity_descriptor, .read_merkle_tree_page = ext4_read_merkle_tree_page, .write_merkle_tree_block = ext4_write_merkle_tree_block, };