--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/verify.c: data verification functions, i.e. hooks for ->readpages()
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <crypto/hash.h>
+#include <linux/bio.h>
+#include <linux/ratelimit.h>
+
+static struct workqueue_struct *fsverity_read_workqueue;
+
+/**
+ * hash_at_level() - compute the location of the block's hash at the given level
+ *
+ * @params: (in) the Merkle tree parameters
+ * @dindex: (in) the index of the data block being verified
+ * @level: (in) the level of hash we want (0 is leaf level)
+ * @hindex: (out) the index of the hash block containing the wanted hash
+ * @hoffset: (out) the byte offset to the wanted hash within the hash block
+ */
+static void hash_at_level(const struct merkle_tree_params *params,
+ pgoff_t dindex, unsigned int level, pgoff_t *hindex,
+ unsigned int *hoffset)
+{
+ pgoff_t position;
+
+ /* Offset of the hash within the level's region, in hashes */
+ position = dindex >> (level * params->log_arity);
+
+ /* Index of the hash block in the tree overall */
+ *hindex = params->level_start[level] + (position >> params->log_arity);
+
+ /* Offset of the wanted hash (in bytes) within the hash block */
+ *hoffset = (position & ((1 << params->log_arity) - 1)) <<
+ (params->log_blocksize - params->log_arity);
+}
+
+/* Extract a hash from a hash page */
+static void extract_hash(struct page *hpage, unsigned int hoffset,
+ unsigned int hsize, u8 *out)
+{
+ void *virt = kmap_atomic(hpage);
+
+ memcpy(out, virt + hoffset, hsize);
+ kunmap_atomic(virt);
+}
+
+static inline int cmp_hashes(const struct fsverity_info *vi,
+ const u8 *want_hash, const u8 *real_hash,
+ pgoff_t index, int level)
+{
+ const unsigned int hsize = vi->tree_params.digest_size;
+
+ if (memcmp(want_hash, real_hash, hsize) == 0)
+ return 0;
+
+ fsverity_err(vi->inode,
+ "FILE CORRUPTED! index=%lu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",
+ index, level,
+ vi->tree_params.hash_alg->name, hsize, want_hash,
+ vi->tree_params.hash_alg->name, hsize, real_hash);
+ return -EBADMSG;
+}
+
+/*
+ * Verify a single data page 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 pages. Therefore we need
+ * only ascend the tree until an already-verified page is seen, as indicated by
+ * the PageChecked bit being set; then verify the path to that page.
+ *
+ * This code currently only supports the case where the verity block size is
+ * equal to PAGE_SIZE. Doing otherwise would be possible but tricky, since we
+ * wouldn't be able to use the PageChecked bit.
+ *
+ * Note that multiple processes may race to verify a hash page and mark it
+ * Checked, but it doesn't matter; the result will be the same either way.
+ *
+ * Return: true if the page is valid, else false.
+ */
+static bool verify_page(struct inode *inode, const struct fsverity_info *vi,
+ struct ahash_request *req, struct page *data_page)
+{
+ const struct merkle_tree_params *params = &vi->tree_params;
+ const unsigned int hsize = params->digest_size;
+ const pgoff_t index = data_page->index;
+ int level;
+ u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];
+ const u8 *want_hash;
+ u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];
+ struct page *hpages[FS_VERITY_MAX_LEVELS];
+ unsigned int hoffsets[FS_VERITY_MAX_LEVELS];
+ int err;
+
+ if (WARN_ON_ONCE(!PageLocked(data_page) || PageUptodate(data_page)))
+ return false;
+
+ pr_debug_ratelimited("Verifying data page %lu...\n", index);
+
+ /*
+ * Starting at the leaf level, ascend the tree saving hash pages along
+ * the way until we find a verified hash page, indicated by PageChecked;
+ * or until we reach the root.
+ */
+ for (level = 0; level < params->num_levels; level++) {
+ pgoff_t hindex;
+ unsigned int hoffset;
+ struct page *hpage;
+
+ hash_at_level(params, index, level, &hindex, &hoffset);
+
+ pr_debug_ratelimited("Level %d: hindex=%lu, hoffset=%u\n",
+ level, hindex, hoffset);
+
+ hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode,
+ hindex);
+ if (IS_ERR(hpage)) {
+ err = PTR_ERR(hpage);
+ fsverity_err(inode,
+ "Error %d reading Merkle tree page %lu",
+ err, hindex);
+ goto out;
+ }
+
+ if (PageChecked(hpage)) {
+ extract_hash(hpage, hoffset, hsize, _want_hash);
+ want_hash = _want_hash;
+ put_page(hpage);
+ pr_debug_ratelimited("Hash page already checked, want %s:%*phN\n",
+ params->hash_alg->name,
+ hsize, want_hash);
+ goto descend;
+ }
+ pr_debug_ratelimited("Hash page not yet checked\n");
+ hpages[level] = hpage;
+ hoffsets[level] = hoffset;
+ }
+
+ want_hash = vi->root_hash;
+ pr_debug("Want root hash: %s:%*phN\n",
+ params->hash_alg->name, hsize, want_hash);
+descend:
+ /* Descend the tree verifying hash pages */
+ for (; level > 0; level--) {
+ struct page *hpage = hpages[level - 1];
+ unsigned int hoffset = hoffsets[level - 1];
+
+ err = fsverity_hash_page(params, inode, req, hpage, real_hash);
+ if (err)
+ goto out;
+ err = cmp_hashes(vi, want_hash, real_hash, index, level - 1);
+ if (err)
+ goto out;
+ SetPageChecked(hpage);
+ extract_hash(hpage, hoffset, hsize, _want_hash);
+ want_hash = _want_hash;
+ put_page(hpage);
+ pr_debug("Verified hash page at level %d, now want %s:%*phN\n",
+ level - 1, params->hash_alg->name, hsize, want_hash);
+ }
+
+ /* Finally, verify the data page */
+ err = fsverity_hash_page(params, inode, req, data_page, real_hash);
+ if (err)
+ goto out;
+ err = cmp_hashes(vi, want_hash, real_hash, index, -1);
+out:
+ for (; level > 0; level--)
+ put_page(hpages[level - 1]);
+
+ return err == 0;
+}
+
+/**
+ * fsverity_verify_page() - verify a data page
+ *
+ * Verify a page that has just been read from a verity file. The page must be a
+ * pagecache page that is still locked and not yet uptodate.
+ *
+ * Return: true if the page is valid, else false.
+ */
+bool fsverity_verify_page(struct page *page)
+{
+ struct inode *inode = page->mapping->host;
+ const struct fsverity_info *vi = inode->i_verity_info;
+ struct ahash_request *req;
+ bool valid;
+
+ req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS);
+ if (unlikely(!req))
+ return false;
+
+ valid = verify_page(inode, vi, req, page);
+
+ ahash_request_free(req);
+
+ return valid;
+}
+EXPORT_SYMBOL_GPL(fsverity_verify_page);
+
+#ifdef CONFIG_BLOCK
+/**
+ * fsverity_verify_bio() - verify a 'read' bio that has just completed
+ *
+ * Verify a set of pages that have just been read from a verity file. The pages
+ * must be pagecache pages that are still locked and not yet uptodate. Pages
+ * that fail verification are set to the Error state. Verification is skipped
+ * for pages already in the Error state, e.g. due to fscrypt decryption failure.
+ *
+ * This is a helper function for use by the ->readpages() 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 inode *inode = bio_first_page_all(bio)->mapping->host;
+ const struct fsverity_info *vi = inode->i_verity_info;
+ struct ahash_request *req;
+ struct bio_vec *bv;
+ struct bvec_iter_all iter_all;
+
+ req = ahash_request_alloc(vi->tree_params.hash_alg->tfm, GFP_NOFS);
+ if (unlikely(!req)) {
+ bio_for_each_segment_all(bv, bio, iter_all)
+ SetPageError(bv->bv_page);
+ return;
+ }
+
+ bio_for_each_segment_all(bv, bio, iter_all) {
+ struct page *page = bv->bv_page;
+
+ if (!PageError(page) && !verify_page(inode, vi, req, page))
+ SetPageError(page);
+ }
+
+ ahash_request_free(req);
+}
+EXPORT_SYMBOL_GPL(fsverity_verify_bio);
+#endif /* CONFIG_BLOCK */
+
+/**
+ * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue
+ *
+ * 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);
+
+int __init fsverity_init_workqueue(void)
+{
+ /*
+ * Use an unbound workqueue to allow bios to be verified in parallel
+ * even when they happen to complete on the same CPU. This sacrifices
+ * locality, but it's worthwhile since hashing is CPU-intensive.
+ *
+ * Also use a high-priority workqueue to prioritize verification work,
+ * which blocks reads from completing, over regular application tasks.
+ */
+ fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",
+ WQ_UNBOUND | WQ_HIGHPRI,
+ num_online_cpus());
+ if (!fsverity_read_workqueue)
+ return -ENOMEM;
+ return 0;
+}
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