From: Eric Biggers <ebiggers@xxxxxxxxxx>
Add functions that verify data pages that have been read from a
fs-verity file, against that file's Merkle tree. These will be called
from filesystems' ->readpage() and ->readpages() methods.
Since data verification can block, a workqueue is provided for these
methods to enqueue verification work from their bio completion callback.
See the "Verifying data" section of
Documentation/filesystems/fsverity.rst for more information.
Reviewed-by: Theodore Ts'o <tytso@xxxxxxx>
Reviewed-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/verity/Makefile | 3 +-
fs/verity/fsverity_private.h | 5 +
fs/verity/init.c | 8 +
fs/verity/open.c | 6 +
fs/verity/verify.c | 275 +++++++++++++++++++++++++++++++++++
include/linux/fsverity.h | 56 +++++++
6 files changed, 352 insertions(+), 1 deletion(-)
create mode 100644 fs/verity/verify.c
diff --git a/fs/verity/Makefile b/fs/verity/Makefile
index e6a8951c493a5..7fa628cd5eba2 100644
--- a/fs/verity/Makefile
+++ b/fs/verity/Makefile
@@ -2,4 +2,5 @@
obj-$(CONFIG_FS_VERITY) += hash_algs.o \
init.o \
- open.o
+ open.o \
+ verify.o
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
index c79746ff335e1..eaa2b3b93bbf6 100644
--- a/fs/verity/fsverity_private.h
+++ b/fs/verity/fsverity_private.h
@@ -134,5 +134,10 @@ void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
void fsverity_free_info(struct fsverity_info *vi);
int __init fsverity_init_info_cache(void);
+void __init fsverity_exit_info_cache(void);
+
+/* verify.c */
+
+int __init fsverity_init_workqueue(void);
#endif /* _FSVERITY_PRIVATE_H */
diff --git a/fs/verity/init.c b/fs/verity/init.c
index fff1fd6343357..b593805aafcc8 100644
--- a/fs/verity/init.c
+++ b/fs/verity/init.c
@@ -41,7 +41,15 @@ static int __init fsverity_init(void)
if (err)
return err;
+ err = fsverity_init_workqueue();
+ if (err)
+ goto err_exit_info_cache;
+
pr_debug("Initialized fs-verity\n");
return 0;
+
+err_exit_info_cache:
+ fsverity_exit_info_cache();
+ return err;
}
late_initcall(fsverity_init)
diff --git a/fs/verity/open.c b/fs/verity/open.c
index 2cb2fe8082bff..3636a1ed8e2c4 100644
--- a/fs/verity/open.c
+++ b/fs/verity/open.c
@@ -337,3 +337,9 @@ int __init fsverity_init_info_cache(void)
return -ENOMEM;
return 0;
}
+
+void __init fsverity_exit_info_cache(void)
+{
+ kmem_cache_destroy(fsverity_info_cachep);
+ fsverity_info_cachep = NULL;
+}
diff --git a/fs/verity/verify.c b/fs/verity/verify.c
new file mode 100644
index 0000000000000..62ab8f6a8ea11
--- /dev/null
+++ b/fs/verity/verify.c
@@ -0,0 +1,275 @@
+// 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;
+}
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
index cbd0f84e1620f..95c257cd7ff02 100644
--- a/include/linux/fsverity.h
+++ b/include/linux/fsverity.h
@@ -33,6 +33,23 @@ struct fsverity_operations {
*/
int (*get_verity_descriptor)(struct inode *inode, void *buf,
size_t bufsize);
+
+ /**
+ * Read a Merkle tree page of the given inode.
+ *
+ * @inode: the inode
+ * @index: 0-based index of the page within the Merkle tree
+ *
+ * This can be called at any time on an open verity file, as well as
+ * between ->begin_enable_verity() and ->end_enable_verity(). It may be
+ * called by multiple processes concurrently, even with the same page.
+ *
+ * Note that this must retrieve a *page*, not necessarily a *block*.
+ *
+ * Return: the page on success, ERR_PTR() on failure
+ */
+ struct page *(*read_merkle_tree_page)(struct inode *inode,
+ pgoff_t index);
};
#ifdef CONFIG_FS_VERITY
@@ -49,6 +66,12 @@ extern int fsverity_file_open(struct inode *inode, struct file *filp);
extern int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
extern void fsverity_cleanup_inode(struct inode *inode);
+/* verify.c */
+
+extern bool fsverity_verify_page(struct page *page);
+extern void fsverity_verify_bio(struct bio *bio);
+extern void fsverity_enqueue_verify_work(struct work_struct *work);
+
#else /* !CONFIG_FS_VERITY */
static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
@@ -73,6 +96,39 @@ static inline void fsverity_cleanup_inode(struct inode *inode)
{
}
+/* verify.c */
+
+static inline bool fsverity_verify_page(struct page *page)
+{
+ WARN_ON(1);
+ return false;
+}
+
+static inline void fsverity_verify_bio(struct bio *bio)
+{
+ WARN_ON(1);
+}
+
+static inline void fsverity_enqueue_verify_work(struct work_struct *work)
+{
+ WARN_ON(1);
+}
+
#endif /* !CONFIG_FS_VERITY */
+/**
+ * fsverity_active() - do reads from the inode need to go through fs-verity?
+ *
+ * This checks whether ->i_verity_info has been set.
+ *
+ * Filesystems call this from ->readpages() to check whether the pages need to
+ * be verified or not. Don't use IS_VERITY() for this purpose; it's subject to
+ * a race condition where the file is being read concurrently with
+ * FS_IOC_ENABLE_VERITY completing. (S_VERITY is set before ->i_verity_info.)
+ */
+static inline bool fsverity_active(const struct inode *inode)
+{
+ return fsverity_get_info(inode) != NULL;
+}
+
#endif /* _LINUX_FSVERITY_H */
--
2.22.0
