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

#include "fsverity_private.h"

/* The hash algorithms supported by fs-verity */
const struct fsverity_hash_alg fsverity_hash_algs[] = {
        [FS_VERITY_HASH_ALG_SHA256] = {
                .name = "sha256",
                .digest_size = SHA256_DIGEST_SIZE,
                .block_size = SHA256_BLOCK_SIZE,
                .algo_id = HASH_ALGO_SHA256,
        },
        [FS_VERITY_HASH_ALG_SHA512] = {
                .name = "sha512",
                .digest_size = SHA512_DIGEST_SIZE,
                .block_size = SHA512_BLOCK_SIZE,
                .algo_id = HASH_ALGO_SHA512,
        },
};

/**
 * fsverity_get_hash_alg() - get a hash algorithm by number
 * @inode: optional inode for logging purposes
 * @num: the hash algorithm number
 *
 * Get the struct fsverity_hash_alg for the given hash algorithm number.
 *
 * Return: pointer to the hash alg if it's known, otherwise NULL.
 */
const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
                                                      unsigned int num)
{
        if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
            !fsverity_hash_algs[num].name) {
                fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
                return NULL;
        }
        return &fsverity_hash_algs[num];
}

/**
 * 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
 *
 * Return: the kmalloc()'ed initial hash state, or NULL if out of memory.
 */
union fsverity_hash_ctx *
fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
                            const u8 *salt, size_t salt_size)
{
        u8 *padded_salt = NULL;
        size_t padded_salt_size;
        union fsverity_hash_ctx ctx;
        void *res = NULL;

        /*
         * 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)
                return NULL;
        memcpy(padded_salt, salt, salt_size);

        switch (alg->algo_id) {
        case HASH_ALGO_SHA256:
                sha256_init(&ctx.sha256);
                sha256_update(&ctx.sha256, padded_salt, padded_salt_size);
                res = kmemdup(&ctx.sha256, sizeof(ctx.sha256), GFP_KERNEL);
                break;
        case HASH_ALGO_SHA512:
                sha512_init(&ctx.sha512);
                sha512_update(&ctx.sha512, padded_salt, padded_salt_size);
                res = kmemdup(&ctx.sha512, sizeof(ctx.sha512), GFP_KERNEL);
                break;
        default:
                WARN_ON_ONCE(1);
        }
        kfree(padded_salt);
        return res;
}

/**
 * fsverity_hash_block() - hash a single data or hash block
 * @params: the Merkle tree's parameters
 * @data: virtual address of a buffer containing the block to hash
 * @out: output digest, size 'params->digest_size' bytes
 *
 * Hash a single data or hash block.  The hash is salted if a salt is specified
 * in the Merkle tree parameters.
 */
void fsverity_hash_block(const struct merkle_tree_params *params,
                         const void *data, u8 *out)
{
        union fsverity_hash_ctx ctx;

        if (!params->hashstate) {
                fsverity_hash_buffer(params->hash_alg, data, params->block_size,
                                     out);
                return;
        }

        switch (params->hash_alg->algo_id) {
        case HASH_ALGO_SHA256:
                ctx.sha256 = params->hashstate->sha256;
                sha256_update(&ctx.sha256, data, params->block_size);
                sha256_final(&ctx.sha256, out);
                return;
        case HASH_ALGO_SHA512:
                ctx.sha512 = params->hashstate->sha512;
                sha512_update(&ctx.sha512, data, params->block_size);
                sha512_final(&ctx.sha512, out);
                return;
        default:
                BUG();
        }
}

/**
 * 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
 */
void fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
                          const void *data, size_t size, u8 *out)
{
        switch (alg->algo_id) {
        case HASH_ALGO_SHA256:
                sha256(data, size, out);
                return;
        case HASH_ALGO_SHA512:
                sha512(data, size, out);
                return;
        default:
                BUG();
        }
}

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;

                /*
                 * 0 must never be allocated as an FS_VERITY_HASH_ALG_* value,
                 * as it is reserved for users that use 0 to mean unspecified or
                 * a default value.  fs/verity/ itself doesn't care and doesn't
                 * have a default algorithm, but some users make use of this.
                 */
                BUG_ON(i == 0);

                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));

                /* Verify that there is a valid mapping to HASH_ALGO_*. */
                BUG_ON(alg->algo_id == 0);
                BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
        }
}