dm-bht.c

 /*
 * Copyright (C) 2010 The Chromium OS Authors <chromium-os-dev@chromium.org>
 *
 * Device-Mapper block hash tree interface.
 * See Documentation/device-mapper/dm-bht.txt for details.
 *
 * This file is released under the GPL.
 */

#include <limits.h>
#include <string.h>

#include <asm/page.h>
#include <linux/bitops.h>  /* for fls() */
#include <linux/bug.h>
/* #define CONFIG_DM_DEBUG 1 */
#include <linux/device-mapper.h>
#include <linux/errno.h>
#include <linux/kernel.h>

#include "verity/dm-bht.h"

#define DM_MSG_PREFIX "dm bht"

/* For sector formatting. */
#if defined(_LP64) || defined(__LP64__) || __BITS_PER_LONG == 64
#define __PRIS_PREFIX "z"
#else
#define __PRIS_PREFIX "ll"
#endif
#define PRIu64 __PRIS_PREFIX "u"

/*-----------------------------------------------
 * Utilities
 *-----------------------------------------------*/

/* We assume we only have one CPU in userland. */
#define nr_cpu_ids 1
#define smp_processor_id(_x) 0

static inline void *alloc_page(void)
{
	void *memptr;

	if (posix_memalign((void **)&memptr, PAGE_SIZE, PAGE_SIZE))
	    return NULL;
	return memptr;
}

static u8 from_hex(u8 ch)
{
	if ((ch >= '0') && (ch <= '9'))
		return ch - '0';
	if ((ch >= 'a') && (ch <= 'f'))
		return ch - 'a' + 10;
	if ((ch >= 'A') && (ch <= 'F'))
		return ch - 'A' + 10;
	return -1;
}

/**
 * dm_bht_bin_to_hex - converts a binary stream to human-readable hex
 * @binary:	a byte array of length @binary_len
 * @hex:	a byte array of length @binary_len * 2 + 1
 */
static void dm_bht_bin_to_hex(u8 *binary, u8 *hex, unsigned int binary_len)
{
	while (binary_len-- > 0) {
                sprintf((char *__restrict__)hex, "%02hhx",
                        (unsigned char)*binary);
		hex += 2;
		binary++;
	}
}

/**
 * dm_bht_hex_to_bin - converts a hex stream to binary
 * @binary:	a byte array of length @binary_len
 * @hex:	a byte array of length @binary_len * 2 + 1
 */
static void dm_bht_hex_to_bin(u8 *binary, const u8 *hex,
			      unsigned int binary_len)
{
	while (binary_len-- > 0) {
		*binary = from_hex(*(hex++));
		*binary *= 16;
		*binary += from_hex(*(hex++));
		binary++;
	}
}

static void dm_bht_log_mismatch(struct dm_bht *bht, u8 *given, u8 *computed)
{
	u8 given_hex[DM_BHT_MAX_DIGEST_SIZE * 2 + 1];
	u8 computed_hex[DM_BHT_MAX_DIGEST_SIZE * 2 + 1];
	dm_bht_bin_to_hex(given, given_hex, bht->digest_size);
	dm_bht_bin_to_hex(computed, computed_hex, bht->digest_size);
	DMERR_LIMIT("%s != %s", given_hex, computed_hex);
}

/* Used for turning verifiers into computers */
typedef int (*dm_bht_compare_cb)(struct dm_bht *, u8 *, u8 *);

/**
 * dm_bht_compute_hash: hashes a page of data
 */
static int dm_bht_compute_hash(struct dm_bht *bht, const u8 *buffer, u8 *digest)
{
	struct hash_desc *hash_desc = &bht->hash_desc[smp_processor_id()];

	/* Note, this is synchronous. */
	if (crypto_hash_init(hash_desc)) {
		DMCRIT("failed to reinitialize crypto hash (proc:%d)",
			smp_processor_id());
		return -EINVAL;
	}
	if (crypto_hash_update(hash_desc, buffer, PAGE_SIZE)) {
		DMCRIT("crypto_hash_update failed");
		return -EINVAL;
	}
	if (bht->have_salt) {
		if (crypto_hash_update(hash_desc, bht->salt, sizeof(bht->salt))) {
			DMCRIT("crypto_hash_update failed");
			return -EINVAL;
		}
	}
	if (crypto_hash_final(hash_desc, digest)) {
		DMCRIT("crypto_hash_final failed");
		return -EINVAL;
	}

	return 0;
}

/*-----------------------------------------------
 * Implementation functions
 *-----------------------------------------------*/

static int dm_bht_initialize_entries(struct dm_bht *bht);

static int dm_bht_read_callback_stub(void *ctx, sector_t start, u8 *dst,
				     sector_t count,
				     struct dm_bht_entry *entry);

/**
 * dm_bht_create - prepares @bht for us
 * @bht:	pointer to a dm_bht_create()d bht
 * @depth:	tree depth without the root; including block hashes
 * @block_count:the number of block hashes / tree leaves
 * @alg_name:	crypto hash algorithm name
 *
 * Returns 0 on success.
 *
 * Callers can offset into devices by storing the data in the io callbacks.
 * TODO(wad) bust up into smaller helpers
 */
int dm_bht_create(struct dm_bht *bht, unsigned int block_count,
		  const char *alg_name)
{
	int status = 0;
	int cpu = 0;

	bht->have_salt = false;

	/* Setup the hash first. Its length determines much of the bht layout */
	for (cpu = 0; cpu < nr_cpu_ids; ++cpu) {
		bht->hash_desc[cpu].tfm = crypto_alloc_hash(alg_name, 0, 0);
		if (bht->hash_desc[cpu].tfm == NULL) {
			DMERR("failed to allocate crypto hash '%s'", alg_name);
			status = -ENOMEM;
			bht->hash_desc[cpu].tfm = NULL;
			goto bad_hash_alg;
		}
	}
	bht->digest_size = crypto_hash_digestsize(bht->hash_desc[0].tfm);
	/* We expect to be able to pack >=2 hashes into a page */
	if (PAGE_SIZE / bht->digest_size < 2) {
		DMERR("too few hashes fit in a page");
		status = -EINVAL;
		goto bad_digest_len;
	}

	if (bht->digest_size > DM_BHT_MAX_DIGEST_SIZE) {
		DMERR("DM_BHT_MAX_DIGEST_SIZE too small for chosen digest");
		status = -EINVAL;
		goto bad_digest_len;
	}

	/* Configure the tree */
	bht->block_count = block_count;
	DMDEBUG("Setting block_count %u", block_count);
	if (block_count == 0) {
		DMERR("block_count must be non-zero");
		status = -EINVAL;
		goto bad_block_count;
	}

	/* Each dm_bht_entry->nodes is one page.  The node code tracks
	 * how many nodes fit into one entry where a node is a single
	 * hash (message digest).
	 */
	bht->node_count_shift = fls(PAGE_SIZE / bht->digest_size) - 1;
	/* Round down to the nearest power of two.  This makes indexing
	 * into the tree much less painful.
	 */
	bht->node_count = 1 << bht->node_count_shift;

	/* This is unlikely to happen, but with 64k pages, who knows. */
	if (bht->node_count > UINT_MAX / bht->digest_size) {
		DMERR("node_count * hash_len exceeds UINT_MAX!");
		status = -EINVAL;
		goto bad_node_count;
	}

	bht->depth = DIV_ROUND_UP(fls(block_count - 1), bht->node_count_shift);
	DMDEBUG("Setting depth to %d.", bht->depth);

	/* Ensure that we can safely shift by this value. */
	if (bht->depth * bht->node_count_shift >= sizeof(unsigned int) * 8) {
		DMERR("specified depth and node_count_shift is too large");
		status = -EINVAL;
		goto bad_node_count;
	}

	/* Allocate levels. Each level of the tree may have an arbitrary number
	 * of dm_bht_entry structs.  Each entry contains node_count nodes.
	 * Each node in the tree is a cryptographic digest of either node_count
	 * nodes on the subsequent level or of a specific block on disk.
	 */
	bht->levels = (struct dm_bht_level *)
			calloc(bht->depth, sizeof(struct dm_bht_level));
	if (!bht->levels) {
		DMERR("failed to allocate tree levels");
		status = -ENOMEM;
		goto bad_level_alloc;
	}

	/* Setup read callback stub */
	bht->read_cb = &dm_bht_read_callback_stub;

	status = dm_bht_initialize_entries(bht);
	if (status)
		goto bad_entries_alloc;

	/* We compute depth such that there is only be 1 block at level 0. */
	BUG_ON(bht->levels[0].count != 1);

	return 0;

bad_entries_alloc:
	while (bht->depth-- > 0)
		free(bht->levels[bht->depth].entries);
	free(bht->levels);
bad_node_count:
bad_level_alloc:
bad_block_count:
bad_digest_len:
bad_hash_alg:
	for (cpu = 0; cpu < nr_cpu_ids; ++cpu)
		if (bht->hash_desc[cpu].tfm)
			crypto_free_hash(bht->hash_desc[cpu].tfm);
	return status;
}

static int dm_bht_initialize_entries(struct dm_bht *bht)
{
	/* The last_index represents the index into the last
	 * block digest that will be stored in the tree.  By walking the
	 * tree with that index, it is possible to compute the total number
	 * of entries needed at each level in the tree.
	 *
	 * Since each entry will contain up to |node_count| nodes of the tree,
	 * it is possible that the last index may not be at the end of a given
	 * entry->nodes.  In that case, it is assumed the value is padded.
	 *
	 * Note, we treat both the tree root (1 hash) and the tree leaves
	 * independently from the bht data structures.  Logically, the root is
	 * depth=-1 and the block layer level is depth=bht->depth
	 */
	unsigned int last_index = ALIGN(bht->block_count, bht->node_count) - 1;
	unsigned int total_entries = 0;
	struct dm_bht_level *level = NULL;
	int depth;

	/* check that the largest level->count can't result in an int overflow
	 * on allocation or sector calculation.
	 */
	if (((last_index >> bht->node_count_shift) + 1) >
	    UINT_MAX / MAX((unsigned int)sizeof(struct dm_bht_entry),
			   (unsigned int)to_sector(PAGE_SIZE))) {
		DMCRIT("required entries %u is too large",
		       last_index + 1);
		return -EINVAL;
	}

	/* Track the current sector location for each level so we don't have to
	 * compute it during traversals.
	 */
	bht->sectors = 0;
	for (depth = 0; depth < bht->depth; ++depth) {
		level = dm_bht_get_level(bht, depth);
		level->count = dm_bht_index_at_level(bht, depth,
						     last_index) + 1;
		DMDEBUG("depth: %d entries: %u", depth, level->count);
		/* TODO(wad) consider the case where the data stored for each
		 * level is done with contiguous pages (instead of using
		 * entry->nodes) and the level just contains two bitmaps:
		 * (a) which pages have been loaded from disk
		 * (b) which specific nodes have been verified.
		 */
		level->entries = (struct dm_bht_entry *)
				 calloc(level->count, sizeof(struct dm_bht_entry));
		if (!level->entries) {
			DMERR("failed to allocate entries for depth %d",
			      bht->depth);
			/* let the caller clean up the mess */
			return -ENOMEM;
		}
		total_entries += level->count;
		level->sector = bht->sectors;
		/* number of sectors per entry * entries at this level */
		bht->sectors += level->count * to_sector(PAGE_SIZE);
		/* not ideal, but since unsigned overflow behavior is defined */
		if (bht->sectors < level->sector) {
			DMCRIT("level sector calculation overflowed");
			return -EINVAL;
		}
	}

	return 0;
}

static int dm_bht_read_callback_stub(void *ctx, sector_t start, u8 *dst,
				     sector_t count, struct dm_bht_entry *entry)
{
	DMCRIT("dm_bht_read_callback_stub called!");
	dm_bht_read_completed(entry, -EIO);
	return -EIO;
}

/**
 * dm_bht_read_completed
 * @entry:	pointer to the entry that's been loaded
 * @status:	I/O status. Non-zero is failure.
 * MUST always be called after a read_cb completes.
 */
void dm_bht_read_completed(struct dm_bht_entry *entry, int status)
{
	if (status) {
		/* TODO(wad) add retry support */
		DMCRIT("an I/O error occurred while reading entry");
		entry->state = DM_BHT_ENTRY_ERROR_IO;
		/* entry->nodes will be freed later */
		return;
	}
	BUG_ON(entry->state != DM_BHT_ENTRY_PENDING);
	entry->state = DM_BHT_ENTRY_READY;
}

/* dm_bht_verify_path
 * Verifies the path. Returns 0 on ok.
 */
static int dm_bht_verify_path(struct dm_bht *bht, unsigned int block,
			      const u8 *buffer)
{
	int depth = bht->depth;
	u8 digest[DM_BHT_MAX_DIGEST_SIZE];
	struct dm_bht_entry *entry;
	u8 *node;
	int state;

	do {
		/* Need to check that the hash of the current block is accurate
		 * in its parent.
		 */
		entry = dm_bht_get_entry(bht, depth - 1, block);
		state = entry->state;
		/* This call is only safe if all nodes along the path
		 * are already populated (i.e. READY) via dm_bht_populate.
		 */
		BUG_ON(state < DM_BHT_ENTRY_READY);
		node = dm_bht_get_node(bht, entry, depth, block);

		if (dm_bht_compute_hash(bht, buffer, digest) ||
		    memcmp(digest, node, bht->digest_size))
			goto mismatch;

		/* Keep the containing block of hashes to be verified in the
		 * next pass.
		 */
		buffer = entry->nodes;
	} while (--depth > 0 && state != DM_BHT_ENTRY_VERIFIED);

	if (depth == 0 && state != DM_BHT_ENTRY_VERIFIED) {
		if (dm_bht_compute_hash(bht, buffer, digest) ||
		    memcmp(digest, bht->root_digest, bht->digest_size))
			goto mismatch;
		entry->state = DM_BHT_ENTRY_VERIFIED;
	}

	/* Mark path to leaf as verified. */
	for (depth++; depth < bht->depth; depth++) {
		entry = dm_bht_get_entry(bht, depth, block);
		/* At this point, entry can only be in VERIFIED or READY state.
		 */
		entry->state = DM_BHT_ENTRY_VERIFIED;
	}

	DMDEBUG("verify_path: node %u is verified to root", block);
	return 0;

mismatch:
	DMERR_LIMIT("verify_path: failed to verify hash (d=%d,bi=%u)",
		    depth, block);
	dm_bht_log_mismatch(bht, node, digest);
	return DM_BHT_ENTRY_ERROR_MISMATCH;
}

/**
 * dm_bht_zeroread_callback - read callback which always returns 0s
 * @ctx:	ignored
 * @start:	ignored
 * @data:	buffer to write 0s to
 * @count:	number of sectors worth of data to write
 * @complete_ctx: opaque context for @completed
 * @completed: callback to confirm end of data read
 *
 * Always returns 0.
 *
 * Meant for use by dm_compute() callers.  It allows dm_populate to
 * be used to pre-fill a tree with zeroed out entry nodes.
 */
int dm_bht_zeroread_callback(void *ctx, sector_t start, u8 *dst,
			     sector_t count, struct dm_bht_entry *entry)
{
	memset(dst, 0, verity_to_bytes(count));
	dm_bht_read_completed(entry, 0);
	return 0;
}

/**
 * dm_bht_is_populated - check that entries from disk needed to verify a given
 *                       block are all ready
 * @bht:	pointer to a dm_bht_create()d bht
 * @block:	specific block data is expected from
 *
 * Callers may wish to call dm_bht_is_populated() when checking an io
 * for which entries were already pending.
 */
bool dm_bht_is_populated(struct dm_bht *bht, unsigned int block)
{
	int depth;

	for (depth = bht->depth - 1; depth >= 0; depth--) {
		struct dm_bht_entry *entry = dm_bht_get_entry(bht, depth,
							      block);
		if (entry->state < DM_BHT_ENTRY_READY)
			return false;
	}

	return true;
}

/**
 * dm_bht_populate - reads entries from disk needed to verify a given block
 * @bht:	pointer to a dm_bht_create()d bht
 * @ctx:        context used for all read_cb calls on this request
 * @block:	specific block data is expected from
 *
 * Returns negative value on error. Returns 0 on success.
 */
int dm_bht_populate(struct dm_bht *bht, void *ctx,
		    unsigned int block)
{
	int depth;
	int state = 0;

	BUG_ON(block >= bht->block_count);

	DMDEBUG("dm_bht_populate(%u)", block);

	for (depth = bht->depth - 1; depth >= 0; --depth) {
		struct dm_bht_level *level;
		struct dm_bht_entry *entry;
		unsigned int index;
		u8 *buffer;

		entry = dm_bht_get_entry(bht, depth, block);
		state = entry->state;
		if (state == DM_BHT_ENTRY_UNALLOCATED)
			entry->state = DM_BHT_ENTRY_PENDING;

		if (state == DM_BHT_ENTRY_VERIFIED)
			break;
		if (state <= DM_BHT_ENTRY_ERROR)
			goto error_state;
		if (state != DM_BHT_ENTRY_UNALLOCATED)
			continue;

		/* Current entry is claimed for allocation and loading */
		buffer = (u8 *)alloc_page();
		if (!buffer)
			goto nomem;

		/* dm-bht guarantees page-aligned memory for callbacks. */
		entry->nodes = buffer;

		/* TODO(wad) error check callback here too */

		level = &bht->levels[depth];
		index = dm_bht_index_at_level(bht, depth, block);
		bht->read_cb(ctx, level->sector + to_sector(index * PAGE_SIZE),
			     entry->nodes, to_sector(PAGE_SIZE), entry);
	}

	return 0;

error_state:
	DMCRIT("block %u at depth %d is in an error state", block, depth);
	return state;

nomem:
	DMCRIT("failed to allocate memory for entry->nodes");
	return -ENOMEM;
}


/**
 * dm_bht_verify_block - checks that all nodes in the path for @block are valid
 * @bht:	pointer to a dm_bht_create()d bht
 * @block:	specific block data is expected from
 * @buffer:	page holding the block data
 * @offset:	offset into the page
 *
 * Returns 0 on success, 1 on missing data, and a negative error
 * code on verification failure. All supporting functions called
 * should return similarly.
 */
int dm_bht_verify_block(struct dm_bht *bht, unsigned int block,
			const u8 *buffer, unsigned int offset)
{
	BUG_ON(offset != 0);

	return dm_bht_verify_path(bht, block, buffer);
}

/**
 * dm_bht_destroy - cleans up all memory used by @bht
 * @bht:	pointer to a dm_bht_create()d bht
 *
 * Returns 0 on success. Does not free @bht itself.
 */
int dm_bht_destroy(struct dm_bht *bht)
{
	int depth;
	int cpu = 0;

	depth = bht->depth;
	while (depth-- != 0) {
		struct dm_bht_entry *entry = bht->levels[depth].entries;
		struct dm_bht_entry *entry_end = entry +
						 bht->levels[depth].count;
		for (; entry < entry_end; ++entry) {
			switch (entry->state) {
			/* At present, no other states free memory,
			 * but that will change.
			 */
			case DM_BHT_ENTRY_UNALLOCATED:
				/* Allocated with improper state */
				BUG_ON(entry->nodes);
				continue;
			default:
				BUG_ON(!entry->nodes);
				free(entry->nodes);
				break;
			}
		}
		free(bht->levels[depth].entries);
		bht->levels[depth].entries = NULL;
	}
	free(bht->levels);
	for (cpu = 0; cpu < nr_cpu_ids; ++cpu)
		if (bht->hash_desc[cpu].tfm)
			crypto_free_hash(bht->hash_desc[cpu].tfm);
	return 0;
}

/*-----------------------------------------------
 * Accessors
 *-----------------------------------------------*/

/**
 * dm_bht_sectors - return the sectors required on disk
 * @bht:	pointer to a dm_bht_create()d bht
 */
sector_t dm_bht_sectors(const struct dm_bht *bht)
{
	return bht->sectors;
}

/**
 * dm_bht_set_read_cb - set read callback
 * @bht:	pointer to a dm_bht_create()d bht
 * @read_cb:	callback function used for all read requests by @bht
 */
void dm_bht_set_read_cb(struct dm_bht *bht, dm_bht_callback read_cb)
{
	bht->read_cb = read_cb;
}

/**
 * dm_bht_set_root_hexdigest - sets an unverified root digest hash from hex
 * @bht:	pointer to a dm_bht_create()d bht
 * @hexdigest:	array of u8s containing the new digest in binary
 * Returns non-zero on error.  hexdigest should be NUL terminated.
 */
int dm_bht_set_root_hexdigest(struct dm_bht *bht, const u8 *hexdigest)
{
	/* Make sure we have at least the bytes expected */
	if (strnlen((char *)hexdigest, bht->digest_size * 2) !=
	    bht->digest_size * 2) {
		DMERR("root digest length does not match hash algorithm");
		return -1;
	}
	dm_bht_hex_to_bin(bht->root_digest, hexdigest, bht->digest_size);
#ifdef CONFIG_DM_DEBUG
	DMINFO("Set root digest to %s. Parsed as -> ", hexdigest);
	dm_bht_log_mismatch(bht, bht->root_digest, bht->root_digest);
#endif
	return 0;
}

/**
 * dm_bht_root_hexdigest - returns root digest in hex
 * @bht:	pointer to a dm_bht_create()d bht
 * @hexdigest:	u8 array of size @available
 * @available:	must be bht->digest_size * 2 + 1
 */
int dm_bht_root_hexdigest(struct dm_bht *bht, u8 *hexdigest, int available)
{
	if (available < 0 ||
	    ((unsigned int) available) < bht->digest_size * 2 + 1) {
		DMERR("hexdigest has too few bytes available");
		return -EINVAL;
	}
	dm_bht_bin_to_hex(bht->root_digest, hexdigest, bht->digest_size);
	return 0;
}

/**
 * dm_bht_set_salt - sets the salt used, in hex
 * @bht:      pointer to a dm_bht_create()d bht
 * @hexsalt:  salt string, as hex; will be zero-padded or truncated to
 *            DM_BHT_SALT_SIZE * 2 hex digits.
 */
void dm_bht_set_salt(struct dm_bht *bht, const char *hexsalt)
{
	size_t saltlen = MIN(strlen(hexsalt) / 2, sizeof(bht->salt));
	bht->have_salt = true;
	memset(bht->salt, 0, sizeof(bht->salt));
	dm_bht_hex_to_bin(bht->salt, (const u8 *)hexsalt, saltlen);
}

/**
 * dm_bht_salt - returns the salt used, in hex
 * @bht:      pointer to a dm_bht_create()d bht
 * @hexsalt:  buffer to put salt into, of length DM_BHT_SALT_SIZE * 2 + 1.
 */
int dm_bht_salt(struct dm_bht *bht, char *hexsalt)
{
	if (!bht->have_salt)
		return -EINVAL;
	dm_bht_bin_to_hex(bht->salt, (u8 *)hexsalt, sizeof(bht->salt));
	return 0;
}