Commit 8a1d0f9c authored by Eric Biggers's avatar Eric Biggers

fs-verity: add data verification hooks for ->readpages()

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: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarJaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
parent c1d9b584
...@@ -2,4 +2,5 @@ ...@@ -2,4 +2,5 @@
obj-$(CONFIG_FS_VERITY) += hash_algs.o \ obj-$(CONFIG_FS_VERITY) += hash_algs.o \
init.o \ init.o \
open.o open.o \
verify.o
...@@ -134,5 +134,10 @@ void fsverity_set_info(struct inode *inode, struct fsverity_info *vi); ...@@ -134,5 +134,10 @@ void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
void fsverity_free_info(struct fsverity_info *vi); void fsverity_free_info(struct fsverity_info *vi);
int __init fsverity_init_info_cache(void); 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 */ #endif /* _FSVERITY_PRIVATE_H */
...@@ -41,7 +41,15 @@ static int __init fsverity_init(void) ...@@ -41,7 +41,15 @@ static int __init fsverity_init(void)
if (err) if (err)
return err; return err;
err = fsverity_init_workqueue();
if (err)
goto err_exit_info_cache;
pr_debug("Initialized fs-verity\n"); pr_debug("Initialized fs-verity\n");
return 0; return 0;
err_exit_info_cache:
fsverity_exit_info_cache();
return err;
} }
late_initcall(fsverity_init) late_initcall(fsverity_init)
...@@ -337,3 +337,9 @@ int __init fsverity_init_info_cache(void) ...@@ -337,3 +337,9 @@ int __init fsverity_init_info_cache(void)
return -ENOMEM; return -ENOMEM;
return 0; return 0;
} }
void __init fsverity_exit_info_cache(void)
{
kmem_cache_destroy(fsverity_info_cachep);
fsverity_info_cachep = 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;
}
...@@ -33,6 +33,23 @@ struct fsverity_operations { ...@@ -33,6 +33,23 @@ struct fsverity_operations {
*/ */
int (*get_verity_descriptor)(struct inode *inode, void *buf, int (*get_verity_descriptor)(struct inode *inode, void *buf,
size_t bufsize); 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 #ifdef CONFIG_FS_VERITY
...@@ -49,6 +66,12 @@ extern int fsverity_file_open(struct inode *inode, struct file *filp); ...@@ -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 int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
extern void fsverity_cleanup_inode(struct inode *inode); 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 */ #else /* !CONFIG_FS_VERITY */
static inline struct fsverity_info *fsverity_get_info(const struct inode *inode) 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) ...@@ -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 */ #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 */ #endif /* _LINUX_FSVERITY_H */
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment