// SPDX-License-Identifier: GPL-2.0
/*
 * fs/verity/hash_algs.c: fs-verity hash algorithms
 *
 * Copyright 2019 Google LLC
 */

#include "fsverity_private.h"

#include <crypto/hash.h>
#include <linux/scatterlist.h>

/* The hash algorithms supported by fs-verity */
struct fsverity_hash_alg fsverity_hash_algs[] = {
        [FS_VERITY_HASH_ALG_SHA256] = {
                .name = "sha256",
                .digest_size = SHA256_DIGEST_SIZE,
                .block_size = SHA256_BLOCK_SIZE,
        },
        [FS_VERITY_HASH_ALG_SHA512] = {
                .name = "sha512",
                .digest_size = SHA512_DIGEST_SIZE,
                .block_size = SHA512_BLOCK_SIZE,
        },
};

/**
 * fsverity_get_hash_alg() - validate and prepare a hash algorithm
 * @inode: optional inode for logging purposes
 * @num: the hash algorithm number
 *
 * Get the struct fsverity_hash_alg for the given hash algorithm number, and
 * ensure it has a hash transform ready to go.  The hash transforms are
 * allocated on-demand so that we don't waste resources unnecessarily, and
 * because the crypto modules may be initialized later than fs/verity/.
 *
 * Return: pointer to the hash alg on success, else an ERR_PTR()
 */
const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
                                                      unsigned int num)
{
        struct fsverity_hash_alg *alg;
        struct crypto_ahash *tfm;
        int err;

        if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
            !fsverity_hash_algs[num].name) {
                fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
                return ERR_PTR(-EINVAL);
        }
        alg = &fsverity_hash_algs[num];

        /* pairs with cmpxchg() below */
        tfm = READ_ONCE(alg->tfm);
        if (likely(tfm != NULL))
                return alg;
        /*
         * Using the shash API would make things a bit simpler, but the ahash
         * API is preferable as it allows the use of crypto accelerators.
         */
        tfm = crypto_alloc_ahash(alg->name, 0, 0);
        if (IS_ERR(tfm)) {
                if (PTR_ERR(tfm) == -ENOENT) {
                        fsverity_warn(inode,
                                      "Missing crypto API support for hash algorithm \"%s\"",
                                      alg->name);
                        return ERR_PTR(-ENOPKG);
                }
                fsverity_err(inode,
                             "Error allocating hash algorithm \"%s\": %ld",
                             alg->name, PTR_ERR(tfm));
                return ERR_CAST(tfm);
        }

        err = -EINVAL;
        if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
                goto err_free_tfm;
        if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
                goto err_free_tfm;

        pr_info("%s using implementation \"%s\"\n",
                alg->name, crypto_ahash_driver_name(tfm));

        /* pairs with READ_ONCE() above */
        if (cmpxchg(&alg->tfm, NULL, tfm) != NULL)
                crypto_free_ahash(tfm);

        return alg;

err_free_tfm:
        crypto_free_ahash(tfm);
        return ERR_PTR(err);
}

/**
 * fsverity_prepare_hash_state() - precompute the initial hash state
 * @alg: hash algorithm
 * @salt: a salt which is to be prepended to all data to be hashed
 * @salt_size: salt size in bytes, possibly 0
 *
 * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed
 *         initial hash state on success or an ERR_PTR() on failure.
 */
const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
                                      const u8 *salt, size_t salt_size)
{
        u8 *hashstate = NULL;
        struct ahash_request *req = NULL;
        u8 *padded_salt = NULL;
        size_t padded_salt_size;
        struct scatterlist sg;
        DECLARE_CRYPTO_WAIT(wait);
        int err;

        if (salt_size == 0)
                return NULL;

        hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL);
        if (!hashstate)
                return ERR_PTR(-ENOMEM);

        req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
        if (!req) {
                err = -ENOMEM;
                goto err_free;
        }

        /*
         * Zero-pad the salt to the next multiple of the input size of the hash
         * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
         * bytes for SHA-512.  This ensures that the hash algorithm won't have
         * any bytes buffered internally after processing the salt, thus making
         * salted hashing just as fast as unsalted hashing.
         */
        padded_salt_size = round_up(salt_size, alg->block_size);
        padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
        if (!padded_salt) {
                err = -ENOMEM;
                goto err_free;
        }
        memcpy(padded_salt, salt, salt_size);

        sg_init_one(&sg, padded_salt, padded_salt_size);
        ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
                                        CRYPTO_TFM_REQ_MAY_BACKLOG,
                                   crypto_req_done, &wait);
        ahash_request_set_crypt(req, &sg, NULL, padded_salt_size);

        err = crypto_wait_req(crypto_ahash_init(req), &wait);
        if (err)
                goto err_free;

        err = crypto_wait_req(crypto_ahash_update(req), &wait);
        if (err)
                goto err_free;

        err = crypto_ahash_export(req, hashstate);
        if (err)
                goto err_free;
out:
        ahash_request_free(req);
        kfree(padded_salt);
        return hashstate;

err_free:
        kfree(hashstate);
        hashstate = ERR_PTR(err);
        goto out;
}

/**
 * fsverity_hash_page() - hash a single data or hash page
 * @params: the Merkle tree's parameters
 * @inode: inode for which the hashing is being done
 * @req: preallocated hash request
 * @page: the page to hash
 * @out: output digest, size 'params->digest_size' bytes
 *
 * Hash a single data or hash block, assuming block_size == PAGE_SIZE.
 * The hash is salted if a salt is specified in the Merkle tree parameters.
 *
 * Return: 0 on success, -errno on failure
 */
int fsverity_hash_page(const struct merkle_tree_params *params,
                       const struct inode *inode,
                       struct ahash_request *req, struct page *page, u8 *out)
{
        struct scatterlist sg;
        DECLARE_CRYPTO_WAIT(wait);
        int err;

        if (WARN_ON(params->block_size != PAGE_SIZE))
                return -EINVAL;

        sg_init_table(&sg, 1);
        sg_set_page(&sg, page, PAGE_SIZE, 0);
        ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
                                        CRYPTO_TFM_REQ_MAY_BACKLOG,
                                   crypto_req_done, &wait);
        ahash_request_set_crypt(req, &sg, out, PAGE_SIZE);

        if (params->hashstate) {
                err = crypto_ahash_import(req, params->hashstate);
                if (err) {
                        fsverity_err(inode,
                                     "Error %d importing hash state", err);
                        return err;
                }
                err = crypto_ahash_finup(req);
        } else {
                err = crypto_ahash_digest(req);
        }

        err = crypto_wait_req(err, &wait);
        if (err)
                fsverity_err(inode, "Error %d computing page hash", err);
        return err;
}

/**
 * fsverity_hash_buffer() - hash some data
 * @alg: the hash algorithm to use
 * @data: the data to hash
 * @size: size of data to hash, in bytes
 * @out: output digest, size 'alg->digest_size' bytes
 *
 * Hash some data which is located in physically contiguous memory (i.e. memory
 * allocated by kmalloc(), not by vmalloc()).  No salt is used.
 *
 * Return: 0 on success, -errno on failure
 */
int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
                         const void *data, size_t size, u8 *out)
{
        struct ahash_request *req;
        struct scatterlist sg;
        DECLARE_CRYPTO_WAIT(wait);
        int err;

        req = ahash_request_alloc(alg->tfm, GFP_KERNEL);
        if (!req)
                return -ENOMEM;

        sg_init_one(&sg, data, size);
        ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP |
                                        CRYPTO_TFM_REQ_MAY_BACKLOG,
                                   crypto_req_done, &wait);
        ahash_request_set_crypt(req, &sg, out, size);

        err = crypto_wait_req(crypto_ahash_digest(req), &wait);

        ahash_request_free(req);
        return err;
}

void __init fsverity_check_hash_algs(void)
{
        size_t i;

        /*
         * Sanity check the hash algorithms (could be a build-time check, but
         * they're in an array)
         */
        for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
                const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];

                if (!alg->name)
                        continue;

                BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);

                /*
                 * For efficiency, the implementation currently assumes the
                 * digest and block sizes are powers of 2.  This limitation can
                 * be lifted if the code is updated to handle other values.
                 */
                BUG_ON(!is_power_of_2(alg->digest_size));
                BUG_ON(!is_power_of_2(alg->block_size));
        }
}