1 /*
2 * Copyright (C) 2021 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 use std::io;
18
19 use thiserror::Error;
20
21 use super::sys::{FS_VERITY_HASH_ALG_SHA256, FS_VERITY_LOG_BLOCKSIZE, FS_VERITY_VERSION};
22 use crate::common::{divide_roundup, CHUNK_SIZE};
23 use crate::crypto::{CryptoError, Sha256Hash, Sha256Hasher};
24
25 #[derive(Error, Debug)]
26 pub enum FsverityError {
27 #[error("Invalid digest")]
28 InvalidDigest,
29 #[error("Insufficient data, only got {0}")]
30 InsufficientData(usize),
31 #[error("Cannot verify a block")]
32 CannotVerify,
33 #[error("I/O error")]
34 Io(#[from] io::Error),
35 #[error("Crypto")]
36 UnexpectedCryptoError(#[from] CryptoError),
37 #[error("Invalid state")]
38 InvalidState,
39 }
40
log128_ceil(num: u64) -> Option<u64>41 fn log128_ceil(num: u64) -> Option<u64> {
42 match num {
43 0 => None,
44 n => Some(divide_roundup(64 - (n - 1).leading_zeros() as u64, 7)),
45 }
46 }
47
48 /// Return the Merkle tree height for our tree configuration, or None if the size is 0.
merkle_tree_height(data_size: u64) -> Option<u64>49 pub fn merkle_tree_height(data_size: u64) -> Option<u64> {
50 let hashes_per_node = CHUNK_SIZE / Sha256Hasher::HASH_SIZE as u64;
51 let hash_pages = divide_roundup(data_size, hashes_per_node * CHUNK_SIZE);
52 log128_ceil(hash_pages)
53 }
54
55 /// Returns the size of Merkle tree for `data_size` bytes amount of data.
merkle_tree_size(mut data_size: u64) -> u6456 pub fn merkle_tree_size(mut data_size: u64) -> u64 {
57 let mut total = 0;
58 while data_size > CHUNK_SIZE {
59 let hash_size = divide_roundup(data_size, CHUNK_SIZE) * Sha256Hasher::HASH_SIZE as u64;
60 let hash_storage_size = divide_roundup(hash_size, CHUNK_SIZE) * CHUNK_SIZE;
61 total += hash_storage_size;
62 data_size = hash_storage_size;
63 }
64 total
65 }
66
build_fsverity_digest( root_hash: &Sha256Hash, file_size: u64, ) -> Result<Sha256Hash, CryptoError>67 pub fn build_fsverity_digest(
68 root_hash: &Sha256Hash,
69 file_size: u64,
70 ) -> Result<Sha256Hash, CryptoError> {
71 // Little-endian byte representation of fsverity_descriptor from linux/fsverity.h
72 // Not FFI-ed as it seems easier to deal with the raw bytes manually.
73 Sha256Hasher::new()?
74 .update(&FS_VERITY_VERSION.to_le_bytes())? // version
75 .update(&FS_VERITY_HASH_ALG_SHA256.to_le_bytes())? // hash_algorithm
76 .update(&FS_VERITY_LOG_BLOCKSIZE.to_le_bytes())? // log_blocksize
77 .update(&0u8.to_le_bytes())? // salt_size
78 .update(&0u32.to_le_bytes())? // sig_size
79 .update(&file_size.to_le_bytes())? // data_size
80 .update(root_hash)? // root_hash, first 32 bytes
81 .update(&[0u8; 32])? // root_hash, last 32 bytes, always 0 because we are using sha256.
82 .update(&[0u8; 32])? // salt
83 .update(&[0u8; 32])? // reserved
84 .update(&[0u8; 32])? // reserved
85 .update(&[0u8; 32])? // reserved
86 .update(&[0u8; 32])? // reserved
87 .update(&[0u8; 16])? // reserved
88 .finalize()
89 }
90
91 #[cfg(test)]
92 mod tests {
93 use super::*;
94
95 #[test]
test_merkle_tree_size()96 fn test_merkle_tree_size() {
97 // To produce groundtruth:
98 // dd if=/dev/zero of=zeros bs=1 count=524289 && \
99 // fsverity digest --out-merkle-tree=tree zeros && \
100 // du -b tree
101 assert_eq!(merkle_tree_size(0), 0);
102 assert_eq!(merkle_tree_size(1), 0);
103 assert_eq!(merkle_tree_size(4096), 0);
104 assert_eq!(merkle_tree_size(4097), 4096);
105 assert_eq!(merkle_tree_size(524288), 4096);
106 assert_eq!(merkle_tree_size(524289), 12288);
107 }
108 }
109