Re: [RFC][PATCH v2 03/13] integrity/digest_cache: Add functions to populate and search

[Jarkko Sakkinen]

On Wed Aug 16, 2023 at 11:35 AM EEST, Roberto Sassu wrote:
> On 8/14/2023 7:13 PM, Jarkko Sakkinen wrote:
> > On Sat Aug 12, 2023 at 1:46 PM EEST, Roberto Sassu wrote:
> >> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> >>
> >> Add digest_cache_init_htable(), to size a hash table depending on the
> >> number of digests to be added to the cache.
> >>
> >> Add digest_cache_add() and digest_cache_lookup() to respectively add and
> >> lookup a digest in the digest cache.
> >>
> >> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> >> ---
> >>   security/integrity/digest_cache.c | 131 ++++++++++++++++++++++++++++++
> >>   security/integrity/digest_cache.h |  24 ++++++
> >>   2 files changed, 155 insertions(+)
> >>
> >> diff --git a/security/integrity/digest_cache.c b/security/integrity/digest_cache.c
> >> index 4201c68171a..d14d84b804b 100644
> >> --- a/security/integrity/digest_cache.c
> >> +++ b/security/integrity/digest_cache.c
> >> @@ -315,3 +315,134 @@ struct digest_cache *digest_cache_get(struct dentry *dentry,
> >>   
> >>   	return iint->dig_user;
> >>   }
> >> +
> >> +/**
> >> + * digest_cache_init_htable - Allocate and initialize the hash table
> >> + * @digest_cache: Digest cache
> >> + * @num_digests: Number of digests to add to the digest cache
> >> + *
> >> + * This function allocates and initializes the hash table. Its size is
> >> + * determined by the number of digests to add to the digest cache, known
> >> + * at this point by the parser calling this function.
> >> + *
> >> + * Return: Zero on success, a negative value otherwise.
> >> + */
> >> +int digest_cache_init_htable(struct digest_cache *digest_cache,
> >> +			     u64 num_digests)
> >> +{
> >> +	int i;
> >> +
> >> +	if (!digest_cache)
> >> +		return 0;
> >> +
> >> +	digest_cache->num_slots = num_digests / DIGEST_CACHE_HTABLE_DEPTH;
> >> +	if (!digest_cache->num_slots)
> >> +		digest_cache->num_slots = 1;
> >> +
> >> +	digest_cache->slots = kmalloc_array(num_digests,
> >> +					    sizeof(*digest_cache->slots),
> >> +					    GFP_KERNEL);
> >> +	if (!digest_cache->slots)
> >> +		return -ENOMEM;
> >> +
> >> +	for (i = 0; i < digest_cache->num_slots; i++)
> >> +		INIT_HLIST_HEAD(&digest_cache->slots[i]);
> >> +
> >> +	pr_debug("Initialized %d hash table slots for digest list %s\n",
> >> +		 digest_cache->num_slots, digest_cache->path_str);
> >> +	return 0;
> >> +}
> >> +
> >> +/**
> >> + * digest_cache_add - Add a new digest to the digest cache
> >> + * @digest_cache: Digest cache
> >> + * @digest: Digest to add
> >> + *
> >> + * This function, invoked by a digest list parser, adds a digest extracted
> >> + * from a digest list to the digest cache.
> >> + *
> >> + * Return: Zero on success, a negative value on error.
> > 
> > Nit: previous had a different phrasing "a negative value otherwise".
> > 
> > I would suggest "a POSIX error code otherwise" for both.
>
> Ok.
>
> >> + */
> >> +int digest_cache_add(struct digest_cache *digest_cache, u8 *digest)
> >> +{
> >> +	struct digest_cache_entry *entry;
> >> +	unsigned int key;
> >> +	int digest_len;
> >> +
> >> +	if (!digest_cache)
> >> +		return 0;
> >> +
> >> +	digest_len = hash_digest_size[digest_cache->algo];
> >> +
> >> +	entry = kmalloc(sizeof(*entry) + digest_len, GFP_KERNEL);
> >> +	if (!entry)
> >> +		return -ENOMEM;
> >> +
> >> +	memcpy(entry->digest, digest, digest_len);
> >> +
> >> +	key = digest_cache_hash_key(digest, digest_cache->num_slots);
> >> +	hlist_add_head(&entry->hnext, &digest_cache->slots[key]);
> >> +	pr_debug("Add digest %s:%*phN from digest list %s\n",
> >> +		 hash_algo_name[digest_cache->algo], digest_len, digest,
> >> +		 digest_cache->path_str);
> >> +	return 0;
> >> +}
> >> +
> >> +/**
> >> + * digest_cache_lookup - Searches a digest in the digest cache
> >> + * @digest_cache: Digest cache
> >> + * @digest: Digest to search
> >> + * @algo: Algorithm of the digest to search
> >> + * @pathname: Path of the file whose digest is looked up
> >> + *
> >> + * This function, invoked by IMA or EVM, searches the calculated digest of
> >> + * a file or file metadata in the digest cache acquired with
> >> + * digest_cache_get().
> >> + *
> >> + * Return: Zero if the digest is found, a negative value if not.
> >> + */
> >> +int digest_cache_lookup(struct digest_cache *digest_cache, u8 *digest,
> >> +			enum hash_algo algo, const char *pathname)
> >> +{
> >> +	struct digest_cache_entry *entry;
> >> +	unsigned int key;
> >> +	int digest_len;
> >> +	int search_depth = 0;
> >> +
> >> +	if (!digest_cache)
> >> +		return -ENOENT;
> >> +
> >> +	if (digest_cache->algo == HASH_ALGO__LAST) {
> >> +		pr_debug("Algorithm not set for digest list %s\n",
> >> +			 digest_cache->path_str);
> >> +		return -ENOENT;
> >> +	}
> >> +
> >> +	digest_len = hash_digest_size[digest_cache->algo];
> >> +
> >> +	if (algo != digest_cache->algo) {
> >> +		pr_debug("Algo mismatch for file %s, digest %s:%*phN in digest list %s (%s)\n",
> >> +			 pathname, hash_algo_name[algo], digest_len, digest,
> >> +			 digest_cache->path_str,
> >> +			 hash_algo_name[digest_cache->algo]);
> >> +		return -ENOENT;
> >> +	}
> >> +
> >> +	key = digest_cache_hash_key(digest, digest_cache->num_slots);
> >> +
> >> +	hlist_for_each_entry_rcu(entry, &digest_cache->slots[key], hnext) {
> >> +		if (!memcmp(entry->digest, digest, digest_len)) {
> >> +			pr_debug("Cache hit at depth %d for file %s, digest %s:%*phN in digest list %s\n",
> >> +				 search_depth, pathname, hash_algo_name[algo],
> >> +				 digest_len, digest, digest_cache->path_str);
> >> +			return 0;
> >> +		}
> >> +
> >> +		search_depth++;
> >> +	}
> >> +
> >> +	pr_debug("Cache miss for file %s, digest %s:%*phN in digest list %s\n",
> >> +		 pathname, hash_algo_name[algo], digest_len, digest,
> >> +		 digest_cache->path_str);
> >> +	return -ENOENT;
> >> +}
> >> diff --git a/security/integrity/digest_cache.h b/security/integrity/digest_cache.h
> >> index ff88e8593c6..01cd70f9850 100644
> >> --- a/security/integrity/digest_cache.h
> >> +++ b/security/integrity/digest_cache.h
> >> @@ -66,6 +66,11 @@ static inline unsigned int digest_cache_hash_key(u8 *digest,
> >>   void digest_cache_free(struct digest_cache *digest_cache);
> >>   struct digest_cache *digest_cache_get(struct dentry *dentry,
> >>   				      struct integrity_iint_cache *iint);
> >> +int digest_cache_init_htable(struct digest_cache *digest_cache,
> >> +			     u64 num_digests);
> >> +int digest_cache_add(struct digest_cache *digest_cache, u8 *digest);
> >> +int digest_cache_lookup(struct digest_cache *digest_cache, u8 *digest,
> >> +			enum hash_algo algo, const char *pathname);
> >>   #else
> >>   static inline void digest_cache_free(struct digest_cache *digest_cache)
> >>   {
> >> @@ -77,5 +82,24 @@ digest_cache_get(struct dentry *dentry, struct integrity_iint_cache *iint)
> >>   	return NULL;
> >>   }
> >>   
> >> +static inline int digest_cache_init_htable(struct digest_cache *digest_cache,
> >> +					   u64 num_digests)
> >> +{
> >> +	return -EOPNOTSUPP;
> >> +}
> >> +
> >> +static inline int digest_cache_add(struct digest_cache *digest_cache,
> >> +				   u8 *digest)
> >> +{
> >> +	return -EOPNOTSUPP;
> >> +}
> >> +
> >> +static inline int digest_cache_lookup(struct digest_cache *digest_cache,
> >> +				      u8 *digest, enum hash_algo algo,
> >> +				      const char *pathname)
> >> +{
> >> +	return -ENOENT;
> >> +}
> >> +
> >>   #endif /* CONFIG_INTEGRITY_DIGEST_CACHE */
> >>   #endif /* _DIGEST_CACHE_H */
> >> -- 
> >> 2.34.1
> > 
> > Why all this complexity instead of using xarray?
> > 
> > https://docs.kernel.org/core-api/xarray.html
>
> Uhm, did I get correctly from the documentation that it isn't the 
> optimal solution for hash tables?

I think you are correct with xarray that it is not a great fit here 
(I overlooked).

BR, Jarkko