WSL2-Linux-Kernel/fs/verity/open.c

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C
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// SPDX-License-Identifier: GPL-2.0
/*
* fs/verity/open.c: opening fs-verity files
*
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
#include <linux/slab.h>
static struct kmem_cache *fsverity_info_cachep;
/**
* fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
* @params: the parameters struct to initialize
* @inode: the inode for which the Merkle tree is being built
* @hash_algorithm: number of hash algorithm to use
* @log_blocksize: log base 2 of block size to use
* @salt: pointer to salt (optional)
* @salt_size: size of salt, possibly 0
*
* Validate the hash algorithm and block size, then compute the tree topology
* (num levels, num blocks in each level, etc.) and initialize @params.
*
* Return: 0 on success, -errno on failure
*/
int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
const struct inode *inode,
unsigned int hash_algorithm,
unsigned int log_blocksize,
const u8 *salt, size_t salt_size)
{
struct fsverity_hash_alg *hash_alg;
int err;
u64 blocks;
u64 offset;
int level;
memset(params, 0, sizeof(*params));
hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
if (IS_ERR(hash_alg))
return PTR_ERR(hash_alg);
params->hash_alg = hash_alg;
params->digest_size = hash_alg->digest_size;
params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
salt_size);
if (IS_ERR(params->hashstate)) {
err = PTR_ERR(params->hashstate);
params->hashstate = NULL;
fsverity_err(inode, "Error %d preparing hash state", err);
goto out_err;
}
if (log_blocksize != PAGE_SHIFT) {
fsverity_warn(inode, "Unsupported log_blocksize: %u",
log_blocksize);
err = -EINVAL;
goto out_err;
}
params->log_blocksize = log_blocksize;
params->block_size = 1 << log_blocksize;
if (WARN_ON(!is_power_of_2(params->digest_size))) {
err = -EINVAL;
goto out_err;
}
if (params->block_size < 2 * params->digest_size) {
fsverity_warn(inode,
"Merkle tree block size (%u) too small for hash algorithm \"%s\"",
params->block_size, hash_alg->name);
err = -EINVAL;
goto out_err;
}
params->log_arity = params->log_blocksize - ilog2(params->digest_size);
params->hashes_per_block = 1 << params->log_arity;
pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
hash_alg->name, params->block_size, params->hashes_per_block,
(int)salt_size, salt);
/*
* Compute the number of levels in the Merkle tree and create a map from
* level to the starting block of that level. Level 'num_levels - 1' is
* the root and is stored first. Level 0 is the level directly "above"
* the data blocks and is stored last.
*/
/* Compute number of levels and the number of blocks in each level */
blocks = (inode->i_size + params->block_size - 1) >> log_blocksize;
pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
while (blocks > 1) {
if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
fsverity_err(inode, "Too many levels in Merkle tree");
err = -EINVAL;
goto out_err;
}
blocks = (blocks + params->hashes_per_block - 1) >>
params->log_arity;
/* temporarily using level_start[] to store blocks in level */
params->level_start[params->num_levels++] = blocks;
}
fs-verity: implement readahead of Merkle tree pages When fs-verity verifies data pages, currently it reads each Merkle tree page synchronously using read_mapping_page(). Therefore, when the Merkle tree pages aren't already cached, fs-verity causes an extra 4 KiB I/O request for every 512 KiB of data (assuming that the Merkle tree uses SHA-256 and 4 KiB blocks). This results in more I/O requests and performance loss than is strictly necessary. Therefore, implement readahead of the Merkle tree pages. For simplicity, we take advantage of the fact that the kernel already does readahead of the file's *data*, just like it does for any other file. Due to this, we don't really need a separate readahead state (struct file_ra_state) just for the Merkle tree, but rather we just need to piggy-back on the existing data readahead requests. We also only really need to bother with the first level of the Merkle tree, since the usual fan-out factor is 128, so normally over 99% of Merkle tree I/O requests are for the first level. Therefore, make fsverity_verify_bio() enable readahead of the first Merkle tree level, for up to 1/4 the number of pages in the bio, when it sees that the REQ_RAHEAD flag is set on the bio. The readahead size is then passed down to ->read_merkle_tree_page() for the filesystem to (optionally) implement if it sees that the requested page is uncached. While we're at it, also make build_merkle_tree_level() set the Merkle tree readahead size, since it's easy to do there. However, for now don't set the readahead size in fsverity_verify_page(), since currently it's only used to verify holes on ext4 and f2fs, and it would need parameters added to know how much to read ahead. This patch significantly improves fs-verity sequential read performance. Some quick benchmarks with 'cat'-ing a 250MB file after dropping caches: On an ARM64 phone (using sha256-ce): Before: 217 MB/s After: 263 MB/s (compare to sha256sum of non-verity file: 357 MB/s) In an x86_64 VM (using sha256-avx2): Before: 173 MB/s After: 215 MB/s (compare to sha256sum of non-verity file: 223 MB/s) Link: https://lore.kernel.org/r/20200106205533.137005-1-ebiggers@kernel.org Reviewed-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Eric Biggers <ebiggers@google.com>
2020-01-06 23:55:33 +03:00
params->level0_blocks = params->level_start[0];
/* Compute the starting block of each level */
offset = 0;
for (level = (int)params->num_levels - 1; level >= 0; level--) {
blocks = params->level_start[level];
params->level_start[level] = offset;
pr_debug("Level %d is %llu blocks starting at index %llu\n",
level, blocks, offset);
offset += blocks;
}
params->tree_size = offset << log_blocksize;
return 0;
out_err:
kfree(params->hashstate);
memset(params, 0, sizeof(*params));
return err;
}
/*
* Compute the file measurement by hashing the fsverity_descriptor excluding the
* signature and with the sig_size field set to 0.
*/
static int compute_file_measurement(struct fsverity_hash_alg *hash_alg,
struct fsverity_descriptor *desc,
u8 *measurement)
{
__le32 sig_size = desc->sig_size;
int err;
desc->sig_size = 0;
err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
desc->sig_size = sig_size;
return err;
}
/*
* Validate the given fsverity_descriptor and create a new fsverity_info from
* it. The signature (if present) is also checked.
*/
struct fsverity_info *fsverity_create_info(const struct inode *inode,
void *_desc, size_t desc_size)
{
struct fsverity_descriptor *desc = _desc;
struct fsverity_info *vi;
int err;
if (desc_size < sizeof(*desc)) {
fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
desc_size);
return ERR_PTR(-EINVAL);
}
if (desc->version != 1) {
fsverity_err(inode, "Unrecognized descriptor version: %u",
desc->version);
return ERR_PTR(-EINVAL);
}
if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
fsverity_err(inode, "Reserved bits set in descriptor");
return ERR_PTR(-EINVAL);
}
if (desc->salt_size > sizeof(desc->salt)) {
fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
return ERR_PTR(-EINVAL);
}
if (le64_to_cpu(desc->data_size) != inode->i_size) {
fsverity_err(inode,
"Wrong data_size: %llu (desc) != %lld (inode)",
le64_to_cpu(desc->data_size), inode->i_size);
return ERR_PTR(-EINVAL);
}
vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
if (!vi)
return ERR_PTR(-ENOMEM);
vi->inode = inode;
err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
desc->hash_algorithm,
desc->log_blocksize,
desc->salt, desc->salt_size);
if (err) {
fsverity_err(inode,
"Error %d initializing Merkle tree parameters",
err);
goto out;
}
memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
err = compute_file_measurement(vi->tree_params.hash_alg, desc,
vi->measurement);
if (err) {
fsverity_err(inode, "Error %d computing file measurement", err);
goto out;
}
pr_debug("Computed file measurement: %s:%*phN\n",
vi->tree_params.hash_alg->name,
vi->tree_params.digest_size, vi->measurement);
err = fsverity_verify_signature(vi, desc, desc_size);
out:
if (err) {
fsverity_free_info(vi);
vi = ERR_PTR(err);
}
return vi;
}
void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
{
/*
* Multiple processes may race to set ->i_verity_info, so use cmpxchg.
* This pairs with the READ_ONCE() in fsverity_get_info().
*/
if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL)
fsverity_free_info(vi);
}
void fsverity_free_info(struct fsverity_info *vi)
{
if (!vi)
return;
kfree(vi->tree_params.hashstate);
kmem_cache_free(fsverity_info_cachep, vi);
}
/* Ensure the inode has an ->i_verity_info */
static int ensure_verity_info(struct inode *inode)
{
struct fsverity_info *vi = fsverity_get_info(inode);
struct fsverity_descriptor *desc;
int res;
if (vi)
return 0;
res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
if (res < 0) {
fsverity_err(inode,
"Error %d getting verity descriptor size", res);
return res;
}
if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
res);
return -EMSGSIZE;
}
desc = kmalloc(res, GFP_KERNEL);
if (!desc)
return -ENOMEM;
res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
if (res < 0) {
fsverity_err(inode, "Error %d reading verity descriptor", res);
goto out_free_desc;
}
vi = fsverity_create_info(inode, desc, res);
if (IS_ERR(vi)) {
res = PTR_ERR(vi);
goto out_free_desc;
}
fsverity_set_info(inode, vi);
res = 0;
out_free_desc:
kfree(desc);
return res;
}
/**
* fsverity_file_open() - prepare to open a verity file
* @inode: the inode being opened
* @filp: the struct file being set up
*
* When opening a verity file, deny the open if it is for writing. Otherwise,
* set up the inode's ->i_verity_info if not already done.
*
* When combined with fscrypt, this must be called after fscrypt_file_open().
* Otherwise, we won't have the key set up to decrypt the verity metadata.
*
* Return: 0 on success, -errno on failure
*/
int fsverity_file_open(struct inode *inode, struct file *filp)
{
if (!IS_VERITY(inode))
return 0;
if (filp->f_mode & FMODE_WRITE) {
pr_debug("Denying opening verity file (ino %lu) for write\n",
inode->i_ino);
return -EPERM;
}
return ensure_verity_info(inode);
}
EXPORT_SYMBOL_GPL(fsverity_file_open);
/**
* fsverity_prepare_setattr() - prepare to change a verity inode's attributes
* @dentry: dentry through which the inode is being changed
* @attr: attributes to change
*
* Verity files are immutable, so deny truncates. This isn't covered by the
* open-time check because sys_truncate() takes a path, not a file descriptor.
*
* Return: 0 on success, -errno on failure
*/
int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
{
if (IS_VERITY(d_inode(dentry)) && (attr->ia_valid & ATTR_SIZE)) {
pr_debug("Denying truncate of verity file (ino %lu)\n",
d_inode(dentry)->i_ino);
return -EPERM;
}
return 0;
}
EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
/**
* fsverity_cleanup_inode() - free the inode's verity info, if present
* @inode: an inode being evicted
*
* Filesystems must call this on inode eviction to free ->i_verity_info.
*/
void fsverity_cleanup_inode(struct inode *inode)
{
fsverity_free_info(inode->i_verity_info);
inode->i_verity_info = NULL;
}
EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
int __init fsverity_init_info_cache(void)
{
fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
SLAB_RECLAIM_ACCOUNT,
measurement);
if (!fsverity_info_cachep)
return -ENOMEM;
return 0;
}
void __init fsverity_exit_info_cache(void)
{
kmem_cache_destroy(fsverity_info_cachep);
fsverity_info_cachep = NULL;
}