fs/verity/hash_algs.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs-verity hash algorithms
   4  *
   5  * Copyright 2019 Google LLC
   6  */
   7
   8 #include "fsverity_private.h"
   9
  10 #include <crypto/hash.h>
  11 #include <linux/scatterlist.h>
  12
  13 /* The hash algorithms supported by fs-verity */
  14 struct fsverity_hash_alg fsverity_hash_algs[] = {
  15         [FS_VERITY_HASH_ALG_SHA256] = {
  16                 .name = "sha256",
  17                 .digest_size = SHA256_DIGEST_SIZE,
  18                 .block_size = SHA256_BLOCK_SIZE,
  19         },
  20         [FS_VERITY_HASH_ALG_SHA512] = {
  21                 .name = "sha512",
  22                 .digest_size = SHA512_DIGEST_SIZE,
  23                 .block_size = SHA512_BLOCK_SIZE,
  24         },
  25 };
  26
  27 static DEFINE_MUTEX(fsverity_hash_alg_init_mutex);
  28
  29 /**
  30  * fsverity_get_hash_alg() - validate and prepare a hash algorithm
  31  * @inode: optional inode for logging purposes
  32  * @num: the hash algorithm number
  33  *
  34  * Get the struct fsverity_hash_alg for the given hash algorithm number, and
  35  * ensure it has a hash transform ready to go.  The hash transforms are
  36  * allocated on-demand so that we don't waste resources unnecessarily, and
  37  * because the crypto modules may be initialized later than fs/verity/.
  38  *
  39  * Return: pointer to the hash alg on success, else an ERR_PTR()
  40  */
  41 struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
  42                                                 unsigned int num)
  43 {
  44         struct fsverity_hash_alg *alg;
  45         struct crypto_ahash *tfm;
  46         int err;
  47
  48         if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
  49             !fsverity_hash_algs[num].name) {
  50                 fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
  51                 return ERR_PTR(-EINVAL);
  52         }
  53         alg = &fsverity_hash_algs[num];
  54
  55         /* pairs with smp_store_release() below */
  56         if (likely(smp_load_acquire(&alg->tfm) != NULL))
  57                 return alg;
  58
  59         mutex_lock(&fsverity_hash_alg_init_mutex);
  60
  61         if (alg->tfm != NULL)
  62                 goto out_unlock;
  63
  64         /*
  65          * Using the shash API would make things a bit simpler, but the ahash
  66          * API is preferable as it allows the use of crypto accelerators.
  67          */
  68         tfm = crypto_alloc_ahash(alg->name, 0, 0);
  69         if (IS_ERR(tfm)) {
  70                 if (PTR_ERR(tfm) == -ENOENT) {
  71                         fsverity_warn(inode,
  72                                       "Missing crypto API support for hash algorithm \"%s\"",
  73                                       alg->name);
  74                         alg = ERR_PTR(-ENOPKG);
  75                         goto out_unlock;
  76                 }
  77                 fsverity_err(inode,
  78                              "Error allocating hash algorithm \"%s\": %ld",
  79                              alg->name, PTR_ERR(tfm));
  80                 alg = ERR_CAST(tfm);
  81                 goto out_unlock;
  82         }
  83
  84         err = -EINVAL;
  85         if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
  86                 goto err_free_tfm;
  87         if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
  88                 goto err_free_tfm;
  89
  90         err = mempool_init_kmalloc_pool(&alg->req_pool, 1,
  91                                         sizeof(struct ahash_request) +
  92                                         crypto_ahash_reqsize(tfm));
  93         if (err)
  94                 goto err_free_tfm;
  95
  96         pr_info("%s using implementation \"%s\"\n",
  97                 alg->name, crypto_ahash_driver_name(tfm));
  98
  99         /* pairs with smp_load_acquire() above */
 100         smp_store_release(&alg->tfm, tfm);
 101         goto out_unlock;
 102
 103 err_free_tfm:
 104         crypto_free_ahash(tfm);
 105         alg = ERR_PTR(err);
 106 out_unlock:
 107         mutex_unlock(&fsverity_hash_alg_init_mutex);
 108         return alg;
 109 }
 110
 111 /**
 112  * fsverity_alloc_hash_request() - allocate a hash request object
 113  * @alg: the hash algorithm for which to allocate the request
 114  * @gfp_flags: memory allocation flags
 115  *
 116  * This is mempool-backed, so this never fails if __GFP_DIRECT_RECLAIM is set in
 117  * @gfp_flags.  However, in that case this might need to wait for all
 118  * previously-allocated requests to be freed.  So to avoid deadlocks, callers
 119  * must never need multiple requests at a time to make forward progress.
 120  *
 121  * Return: the request object on success; NULL on failure (but see above)
 122  */
 123 struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
 124                                                   gfp_t gfp_flags)
 125 {
 126         struct ahash_request *req = mempool_alloc(&alg->req_pool, gfp_flags);
 127
 128         if (req)
 129                 ahash_request_set_tfm(req, alg->tfm);
 130         return req;
 131 }
 132
 133 /**
 134  * fsverity_free_hash_request() - free a hash request object
 135  * @alg: the hash algorithm
 136  * @req: the hash request object to free
 137  */
 138 void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
 139                                 struct ahash_request *req)
 140 {
 141         if (req) {
 142                 ahash_request_zero(req);
 143                 mempool_free(req, &alg->req_pool);
 144         }
 145 }
 146
 147 /**
 148  * fsverity_prepare_hash_state() - precompute the initial hash state
 149  * @alg: hash algorithm
 150  * @salt: a salt which is to be prepended to all data to be hashed
 151  * @salt_size: salt size in bytes, possibly 0
 152  *
 153  * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
 154  *         initial hash state on success or an ERR_PTR() on failure.
 155  */
 156 const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
 157                                       const u8 *salt, size_t salt_size)
 158 {
 159         u8 *hashstate = NULL;
 160         struct ahash_request *req = NULL;
 161         u8 *padded_salt = NULL;
 162         size_t padded_salt_size;
 163         struct scatterlist sg;
 164         DECLARE_CRYPTO_WAIT(wait);
 165         int err;
 166
 167         if (salt_size == 0)
 168                 return NULL;
 169
 170         hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
 171         if (!hashstate)
 172                 return ERR_PTR(-ENOMEM);
 173
 174         /* This allocation never fails, since it's mempool-backed. */
 175         req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
 176
 177         /*
 178          * Zero-pad the salt to the next multiple of the input size of the hash
 179          * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
 180          * bytes for SHA-512.  This ensures that the hash algorithm won't have
 181          * any bytes buffered internally after processing the salt, thus making
 182          * salted hashing just as fast as unsalted hashing.
 183          */
 184         padded_salt_size = round_up(salt_size, alg->block_size);
 185         padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
 186         if (!padded_salt) {
 187                 err = -ENOMEM;
 188                 goto err_free;
 189         }
 190         memcpy(padded_salt, salt, salt_size);
 191
 192         sg_init_one(&sg, padded_salt, padded_salt_size);
 193         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
 194                                         CRYPTO_TFM_REQ_MAY_BACKLOG,
 195                                    crypto_req_done, &wait);
 196         ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);
 197
 198         err = crypto_wait_req(crypto_ahash_init(req), &wait);
 199         if (err)
 200                 goto err_free;
 201
 202         err = crypto_wait_req(crypto_ahash_update(req), &wait);
 203         if (err)
 204                 goto err_free;
 205
 206         err = crypto_ahash_export(req, hashstate);
 207         if (err)
 208                 goto err_free;
 209 out:
 210         fsverity_free_hash_request(alg, req);
 211         kfree(padded_salt);
 212         return hashstate;
 213
 214 err_free:
 215         kfree(hashstate);
 216         hashstate = ERR_PTR(err);
 217         goto out;
 218 }
 219
 220 /**
 221  * fsverity_hash_page() - hash a single data or hash page
 222  * @params: the Merkle tree's parameters
 223  * @inode: inode for which the hashing is being done
 224  * @req: preallocated hash request
 225  * @page: the page to hash
 226  * @out: output digest, size 'params->digest_size' bytes
 227  *
 228  * Hash a single data or hash block, assuming block_size == PAGE_SIZE.
 229  * The hash is salted if a salt is specified in the Merkle tree parameters.
 230  *
 231  * Return: 0 on success, -errno on failure
 232  */
 233 int fsverity_hash_page(const struct merkle_tree_params *params,
 234                        const struct inode *inode,
 235                        struct ahash_request *req, struct page *page, u8 *out)
 236 {
 237         struct scatterlist sg;
 238         DECLARE_CRYPTO_WAIT(wait);
 239         int err;
 240
 241         if (WARN_ON(params->block_size != PAGE_SIZE))
 242                 return -EINVAL;
 243
 244         sg_init_table(&sg, 1);
 245         sg_set_page(&sg, page, PAGE_SIZE, 0);
 246         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
 247                                         CRYPTO_TFM_REQ_MAY_BACKLOG,
 248                                    crypto_req_done, &wait);
 249         ahash_request_set_crypt(req, &sg, out, PAGE_SIZE);
 250
 251         if (params->hashstate) {
 252                 err = crypto_ahash_import(req, params->hashstate);
 253                 if (err) {
 254                         fsverity_err(inode,
 255                                      "Error %d importing hash state", err);
 256                         return err;
 257                 }
 258                 err = crypto_ahash_finup(req);
 259         } else {
 260                 err = crypto_ahash_digest(req);
 261         }
 262
 263         err = crypto_wait_req(err, &wait);
 264         if (err)
 265                 fsverity_err(inode, "Error %d computing page hash", err);
 266         return err;
 267 }
 268
 269 /**
 270  * fsverity_hash_buffer() - hash some data
 271  * @alg: the hash algorithm to use
 272  * @data: the data to hash
 273  * @size: size of data to hash, in bytes
 274  * @out: output digest, size 'alg->digest_size' bytes
 275  *
 276  * Hash some data which is located in physically contiguous memory (i.e. memory
 277  * allocated by kmalloc(), not by vmalloc()).  No salt is used.
 278  *
 279  * Return: 0 on success, -errno on failure
 280  */
 281 int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
 282                          const void *data, size_t size, u8 *out)
 283 {
 284         struct ahash_request *req;
 285         struct scatterlist sg;
 286         DECLARE_CRYPTO_WAIT(wait);
 287         int err;
 288
 289         /* This allocation never fails, since it's mempool-backed. */
 290         req = fsverity_alloc_hash_request(alg, GFP_KERNEL);
 291
 292         sg_init_one(&sg, data, size);
 293         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
 294                                         CRYPTO_TFM_REQ_MAY_BACKLOG,
 295                                    crypto_req_done, &wait);
 296         ahash_request_set_crypt(req, &sg, out, size);
 297
 298         err = crypto_wait_req(crypto_ahash_digest(req), &wait);
 299
 300         fsverity_free_hash_request(alg, req);
 301         return err;
 302 }
 303
 304 void __init fsverity_check_hash_algs(void)
 305 {
 306         size_t i;
 307
 308         /*
 309          * Sanity check the hash algorithms (could be a build-time check, but
 310          * they're in an array)
 311          */
 312         for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
 313                 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
 314
 315                 if (!alg->name)
 316                         continue;
 317
 318                 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
 319
 320                 /*
 321                  * For efficiency, the implementation currently assumes the
 322                  * digest and block sizes are powers of 2.  This limitation can
 323                  * be lifted if the code is updated to handle other values.
 324                  */
 325                 BUG_ON(!is_power_of_2(alg->digest_size));
 326                 BUG_ON(!is_power_of_2(alg->block_size));
 327         }
 328 }