blob: 6c31a871b84bccb472b5008fe304c0dab0ca725f [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
/*
* Opening fs-verity files
*
* Copyright 2019 Google LLC
*/
#include "fsverity_private.h"
#include <linux/mm.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)
{
const struct fsverity_hash_alg *hash_alg;
int err;
u64 blocks;
u64 blocks_in_level[FS_VERITY_MAX_LEVELS];
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;
}
/*
* fs/verity/ directly assumes that the Merkle tree block size is a
* power of 2 less than or equal to PAGE_SIZE. Another restriction
* arises from the interaction between fs/verity/ and the filesystems
* themselves: filesystems expect to be able to verify a single
* filesystem block of data at a time. Therefore, the Merkle tree block
* size must also be less than or equal to the filesystem block size.
*
* The above are the only hard limitations, so in theory the Merkle tree
* block size could be as small as twice the digest size. However,
* that's not useful, and it would result in some unusually deep and
* large Merkle trees. So we currently require that the Merkle tree
* block size be at least 1024 bytes. That's small enough to test the
* sub-page block case on systems with 4K pages, but not too small.
*/
if (log_blocksize < 10 || log_blocksize > PAGE_SHIFT ||
log_blocksize > inode->i_blkbits) {
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;
params->log_blocks_per_page = PAGE_SHIFT - log_blocksize;
params->blocks_per_page = 1 << params->log_blocks_per_page;
if (WARN_ON_ONCE(!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_digestsize = ilog2(params->digest_size);
params->log_arity = log_blocksize - params->log_digestsize;
params->hashes_per_block = 1 << params->log_arity;
/*
* 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 = ((u64)inode->i_size + params->block_size - 1) >> log_blocksize;
while (blocks > 1) {
if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
fsverity_err(inode, "Too many levels in Merkle tree");
err = -EFBIG;
goto out_err;
}
blocks = (blocks + params->hashes_per_block - 1) >>
params->log_arity;
blocks_in_level[params->num_levels++] = blocks;
}
/* Compute the starting block of each level */
offset = 0;
for (level = (int)params->num_levels - 1; level >= 0; level--) {
params->level_start[level] = offset;
offset += blocks_in_level[level];
}
/*
* With block_size != PAGE_SIZE, an in-memory bitmap will need to be
* allocated to track the "verified" status of hash blocks. Don't allow
* this bitmap to get too large. For now, limit it to 1 MiB, which
* limits the file size to about 4.4 TB with SHA-256 and 4K blocks.
*
* Together with the fact that the data, and thus also the Merkle tree,
* cannot have more than ULONG_MAX pages, this implies that hash block
* indices can always fit in an 'unsigned long'. But to be safe, we
* explicitly check for that too. Note, this is only for hash block
* indices; data block indices might not fit in an 'unsigned long'.
*/
if ((params->block_size != PAGE_SIZE && offset > 1 << 23) ||
offset > ULONG_MAX) {
fsverity_err(inode, "Too many blocks in Merkle tree");
err = -EFBIG;
goto out_err;
}
params->tree_size = offset << log_blocksize;
params->tree_pages = PAGE_ALIGN(params->tree_size) >> PAGE_SHIFT;
return 0;
out_err:
kfree(params->hashstate);
memset(params, 0, sizeof(*params));
return err;
}
/*
* Compute the file digest by hashing the fsverity_descriptor excluding the
* builtin signature and with the sig_size field set to 0.
*/
static int compute_file_digest(const struct fsverity_hash_alg *hash_alg,
struct fsverity_descriptor *desc,
u8 *file_digest)
{
__le32 sig_size = desc->sig_size;
int err;
desc->sig_size = 0;
err = fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), file_digest);
desc->sig_size = sig_size;
return err;
}
/*
* Create a new fsverity_info from the given fsverity_descriptor (with optional
* appended builtin signature), and check the signature if present. The
* fsverity_descriptor must have already undergone basic validation.
*/
struct fsverity_info *fsverity_create_info(const struct inode *inode,
struct fsverity_descriptor *desc)
{
struct fsverity_info *vi;
int err;
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 fail;
}
memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
err = compute_file_digest(vi->tree_params.hash_alg, desc,
vi->file_digest);
if (err) {
fsverity_err(inode, "Error %d computing file digest", err);
goto fail;
}
err = fsverity_verify_signature(vi, desc->signature,
le32_to_cpu(desc->sig_size));
if (err)
goto fail;
if (vi->tree_params.block_size != PAGE_SIZE) {
/*
* When the Merkle tree block size and page size differ, we use
* a bitmap to keep track of which hash blocks have been
* verified. This bitmap must contain one bit per hash block,
* including alignment to a page boundary at the end.
*
* Eventually, to support extremely large files in an efficient
* way, it might be necessary to make pages of this bitmap
* reclaimable. But for now, simply allocating the whole bitmap
* is a simple solution that works well on the files on which
* fsverity is realistically used. E.g., with SHA-256 and 4K
* blocks, a 100MB file only needs a 24-byte bitmap, and the
* bitmap for any file under 17GB fits in a 4K page.
*/
unsigned long num_bits =
vi->tree_params.tree_pages <<
vi->tree_params.log_blocks_per_page;
vi->hash_block_verified = kvcalloc(BITS_TO_LONGS(num_bits),
sizeof(unsigned long),
GFP_KERNEL);
if (!vi->hash_block_verified) {
err = -ENOMEM;
goto fail;
}
spin_lock_init(&vi->hash_page_init_lock);
}
return vi;
fail:
fsverity_free_info(vi);
return ERR_PTR(err);
}
void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
{
/*
* Multiple tasks may race to set ->i_verity_info, so use
* cmpxchg_release(). This pairs with the smp_load_acquire() in
* fsverity_get_info(). I.e., here we publish ->i_verity_info with a
* RELEASE barrier so that other tasks can ACQUIRE it.
*/
if (cmpxchg_release(&inode->i_verity_info, NULL, vi) != NULL) {
/* Lost the race, so free the fsverity_info we allocated. */
fsverity_free_info(vi);
/*
* Afterwards, the caller may access ->i_verity_info directly,
* so make sure to ACQUIRE the winning fsverity_info.
*/
(void)fsverity_get_info(inode);
}
}
void fsverity_free_info(struct fsverity_info *vi)
{
if (!vi)
return;
kfree(vi->tree_params.hashstate);
kvfree(vi->hash_block_verified);
kmem_cache_free(fsverity_info_cachep, vi);
}
static bool validate_fsverity_descriptor(struct inode *inode,
const struct fsverity_descriptor *desc,
size_t desc_size)
{
if (desc_size < sizeof(*desc)) {
fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
desc_size);
return false;
}
if (desc->version != 1) {
fsverity_err(inode, "Unrecognized descriptor version: %u",
desc->version);
return false;
}
if (memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
fsverity_err(inode, "Reserved bits set in descriptor");
return false;
}
if (desc->salt_size > sizeof(desc->salt)) {
fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
return false;
}
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 false;
}
if (le32_to_cpu(desc->sig_size) > desc_size - sizeof(*desc)) {
fsverity_err(inode, "Signature overflows verity descriptor");
return false;
}
return true;
}
/*
* Read the inode's fsverity_descriptor (with optional appended builtin
* signature) from the filesystem, and do basic validation of it.
*/
int fsverity_get_descriptor(struct inode *inode,
struct fsverity_descriptor **desc_ret)
{
int res;
struct fsverity_descriptor *desc;
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);
kfree(desc);
return res;
}
if (!validate_fsverity_descriptor(inode, desc, res)) {
kfree(desc);
return -EINVAL;
}
*desc_ret = desc;
return 0;
}
/* 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 err;
if (vi)
return 0;
err = fsverity_get_descriptor(inode, &desc);
if (err)
return err;
vi = fsverity_create_info(inode, desc);
if (IS_ERR(vi)) {
err = PTR_ERR(vi);
goto out_free_desc;
}
fsverity_set_info(inode, vi);
err = 0;
out_free_desc:
kfree(desc);
return err;
}
int __fsverity_file_open(struct inode *inode, struct file *filp)
{
if (filp->f_mode & FMODE_WRITE)
return -EPERM;
return ensure_verity_info(inode);
}
EXPORT_SYMBOL_GPL(__fsverity_file_open);
int __fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
{
if (attr->ia_valid & ATTR_SIZE)
return -EPERM;
return 0;
}
EXPORT_SYMBOL_GPL(__fsverity_prepare_setattr);
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);
void __init fsverity_init_info_cache(void)
{
fsverity_info_cachep = KMEM_CACHE_USERCOPY(
fsverity_info,
SLAB_RECLAIM_ACCOUNT | SLAB_PANIC,
file_digest);
}