// SPDX-License-Identifier: GPL-2.0 /* * Data verification functions, i.e. hooks for ->readahead() * * Copyright 2019 Google LLC */ #include "fsverity_private.h" #include <crypto/hash.h> #include <linux/bio.h> static struct workqueue_struct *fsverity_read_workqueue; /* * Returns true if the hash block with index @hblock_idx in the tree, located in * @hpage, has already been verified. */ static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage, unsigned long hblock_idx) { bool verified; unsigned int blocks_per_page; unsigned int i; /* * When the Merkle tree block size and page size are the same, then the * ->hash_block_verified bitmap isn't allocated, and we use PG_checked * to directly indicate whether the page's block has been verified. * * Using PG_checked also guarantees that we re-verify hash pages that * get evicted and re-instantiated from the backing storage, as new * pages always start out with PG_checked cleared. */ if (!vi->hash_block_verified) return PageChecked(hpage); /* * When the Merkle tree block size and page size differ, we use a bitmap * to indicate whether each hash block has been verified. * * However, we still need to ensure that hash pages that get evicted and * re-instantiated from the backing storage are re-verified. To do * this, we use PG_checked again, but now it doesn't really mean * "checked". Instead, now it just serves as an indicator for whether * the hash page is newly instantiated or not. * * The first thread that sees PG_checked=0 must clear the corresponding * bitmap bits, then set PG_checked=1. This requires a spinlock. To * avoid having to take this spinlock in the common case of * PG_checked=1, we start with an opportunistic lockless read. */ if (PageChecked(hpage)) { /* * A read memory barrier is needed here to give ACQUIRE * semantics to the above PageChecked() test. */ smp_rmb(); return test_bit(hblock_idx, vi->hash_block_verified); } spin_lock(&vi->hash_page_init_lock); if (PageChecked(hpage)) { verified = test_bit(hblock_idx, vi->hash_block_verified); } else { blocks_per_page = vi->tree_params.blocks_per_page; hblock_idx = round_down(hblock_idx, blocks_per_page); for (i = 0; i < blocks_per_page; i++) clear_bit(hblock_idx + i, vi->hash_block_verified); /* * A write memory barrier is needed here to give RELEASE * semantics to the below SetPageChecked() operation. */ smp_wmb(); SetPageChecked(hpage); verified = false; } spin_unlock(&vi->hash_page_init_lock); return verified; } /* * Verify a single data block against the file's Merkle tree. * * In principle, we need to verify the entire path to the root node. However, * for efficiency the filesystem may cache the hash blocks. Therefore we need * only ascend the tree until an already-verified hash block is seen, and then * verify the path to that block. * * Return: %true if the data block is valid, else %false. */ static bool verify_data_block(struct inode *inode, struct fsverity_info *vi, const void *data, u64 data_pos, unsigned long max_ra_pages) { const struct merkle_tree_params *params = &vi->tree_params; const unsigned int hsize = params->digest_size; int level; u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE]; const u8 *want_hash; u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE]; /* The hash blocks that are traversed, indexed by level */ struct { /* Page containing the hash block */ struct page *page; /* Mapped address of the hash block (will be within @page) */ const void *addr; /* Index of the hash block in the tree overall */ unsigned long index; /* Byte offset of the wanted hash relative to @addr */ unsigned int hoffset; } hblocks[FS_VERITY_MAX_LEVELS]; /* * The index of the previous level's block within that level; also the * index of that block's hash within the current level. */ u64 hidx = data_pos >> params->log_blocksize; /* Up to 1 + FS_VERITY_MAX_LEVELS pages may be mapped at once */ BUILD_BUG_ON(1 + FS_VERITY_MAX_LEVELS > KM_MAX_IDX); if (unlikely(data_pos >= inode->i_size)) { /* * This can happen in the data page spanning EOF when the Merkle * tree block size is less than the page size. The Merkle tree * doesn't cover data blocks fully past EOF. But the entire * page spanning EOF can be visible to userspace via a mmap, and * any part past EOF should be all zeroes. Therefore, we need * to verify that any data blocks fully past EOF are all zeroes. */ if (memchr_inv(data, 0, params->block_size)) { fsverity_err(inode, "FILE CORRUPTED! Data past EOF is not zeroed"); return false; } return true; } /* * Starting at the leaf level, ascend the tree saving hash blocks along * the way until we find a hash block that has already been verified, or * until we reach the root. */ for (level = 0; level < params->num_levels; level++) { unsigned long next_hidx; unsigned long hblock_idx; pgoff_t hpage_idx; unsigned int hblock_offset_in_page; unsigned int hoffset; struct page *hpage; const void *haddr; /* * The index of the block in the current level; also the index * of that block's hash within the next level. */ next_hidx = hidx >> params->log_arity; /* Index of the hash block in the tree overall */ hblock_idx = params->level_start[level] + next_hidx; /* Index of the hash page in the tree overall */ hpage_idx = hblock_idx >> params->log_blocks_per_page; /* Byte offset of the hash block within the page */ hblock_offset_in_page = (hblock_idx << params->log_blocksize) & ~PAGE_MASK; /* Byte offset of the hash within the block */ hoffset = (hidx << params->log_digestsize) & (params->block_size - 1); hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode, hpage_idx, level == 0 ? min(max_ra_pages, params->tree_pages - hpage_idx) : 0); if (IS_ERR(hpage)) { fsverity_err(inode, "Error %ld reading Merkle tree page %lu", PTR_ERR(hpage), hpage_idx); goto error; } haddr = kmap_local_page(hpage) + hblock_offset_in_page; if (is_hash_block_verified(vi, hpage, hblock_idx)) { memcpy(_want_hash, haddr + hoffset, hsize); want_hash = _want_hash; kunmap_local(haddr); put_page(hpage); goto descend; } hblocks[level].page = hpage; hblocks[level].addr = haddr; hblocks[level].index = hblock_idx; hblocks[level].hoffset = hoffset; hidx = next_hidx; } want_hash = vi->root_hash; descend: /* Descend the tree verifying hash blocks. */ for (; level > 0; level--) { struct page *hpage = hblocks[level - 1].page; const void *haddr = hblocks[level - 1].addr; unsigned long hblock_idx = hblocks[level - 1].index; unsigned int hoffset = hblocks[level - 1].hoffset; if (fsverity_hash_block(params, inode, haddr, real_hash) != 0) goto error; if (memcmp(want_hash, real_hash, hsize) != 0) goto corrupted; /* * Mark the hash block as verified. This must be atomic and * idempotent, as the same hash block might be verified by * multiple threads concurrently. */ if (vi->hash_block_verified) set_bit(hblock_idx, vi->hash_block_verified); else SetPageChecked(hpage); memcpy(_want_hash, haddr + hoffset, hsize); want_hash = _want_hash; kunmap_local(haddr); put_page(hpage); } /* Finally, verify the data block. */ if (fsverity_hash_block(params, inode, data, real_hash) != 0) goto error; if (memcmp(want_hash, real_hash, hsize) != 0) goto corrupted; return true; corrupted: fsverity_err(inode, "FILE CORRUPTED! pos=%llu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN", data_pos, level - 1, params->hash_alg->name, hsize, want_hash, params->hash_alg->name, hsize, real_hash); error: for (; level > 0; level--) { kunmap_local(hblocks[level - 1].addr); put_page(hblocks[level - 1].page); } return false; } static bool verify_data_blocks(struct folio *data_folio, size_t len, size_t offset, unsigned long max_ra_pages) { struct inode *inode = data_folio->mapping->host; struct fsverity_info *vi = inode->i_verity_info; const unsigned int block_size = vi->tree_params.block_size; u64 pos = (u64)data_folio->index << PAGE_SHIFT; if (WARN_ON_ONCE(len <= 0 || !IS_ALIGNED(len | offset, block_size))) return false; if (WARN_ON_ONCE(!folio_test_locked(data_folio) || folio_test_uptodate(data_folio))) return false; do { void *data; bool valid; data = kmap_local_folio(data_folio, offset); valid = verify_data_block(inode, vi, data, pos + offset, max_ra_pages); kunmap_local(data); if (!valid) return false; offset += block_size; len -= block_size; } while (len); return true; } /** * fsverity_verify_blocks() - verify data in a folio * @folio: the folio containing the data to verify * @len: the length of the data to verify in the folio * @offset: the offset of the data to verify in the folio * * Verify data that has just been read from a verity file. The data must be * located in a pagecache folio that is still locked and not yet uptodate. The * length and offset of the data must be Merkle tree block size aligned. * * Return: %true if the data is valid, else %false. */ bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset) { return verify_data_blocks(folio, len, offset, 0); } EXPORT_SYMBOL_GPL(fsverity_verify_blocks); #ifdef CONFIG_BLOCK /** * fsverity_verify_bio() - verify a 'read' bio that has just completed * @bio: the bio to verify * * Verify the bio's data against the file's Merkle tree. All bio data segments * must be aligned to the file's Merkle tree block size. If any data fails * verification, then bio->bi_status is set to an error status. * * This is a helper function for use by the ->readahead() method of filesystems * that issue bios to read data directly into the page cache. Filesystems that * populate the page cache without issuing bios (e.g. non block-based * filesystems) must instead call fsverity_verify_page() directly on each page. * All filesystems must also call fsverity_verify_page() on holes. */ void fsverity_verify_bio(struct bio *bio) { struct folio_iter fi; unsigned long max_ra_pages = 0; if (bio->bi_opf & REQ_RAHEAD) { /* * If this bio is for data readahead, then we also do readahead * of the first (largest) level of the Merkle tree. Namely, * when a Merkle tree page is read, we also try to piggy-back on * some additional pages -- up to 1/4 the number of data pages. * * This improves sequential read performance, as it greatly * reduces the number of I/O requests made to the Merkle tree. */ max_ra_pages = bio->bi_iter.bi_size >> (PAGE_SHIFT + 2); } bio_for_each_folio_all(fi, bio) { if (!verify_data_blocks(fi.folio, fi.length, fi.offset, max_ra_pages)) { bio->bi_status = BLK_STS_IOERR; break; } } } EXPORT_SYMBOL_GPL(fsverity_verify_bio); #endif /* CONFIG_BLOCK */ /** * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue * @work: the work to enqueue * * Enqueue verification work for asynchronous processing. */ void fsverity_enqueue_verify_work(struct work_struct *work) { queue_work(fsverity_read_workqueue, work); } EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work); void __init fsverity_init_workqueue(void) { /* * Use a high-priority workqueue to prioritize verification work, which * blocks reads from completing, over regular application tasks. * * For performance reasons, don't use an unbound workqueue. Using an * unbound workqueue for crypto operations causes excessive scheduler * latency on ARM64. */ fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue", WQ_HIGHPRI, num_online_cpus()); if (!fsverity_read_workqueue) panic("failed to allocate fsverity_read_queue"); }