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Message-Id: <CUU9SIBEDBLO.1VTU1PCPLLEYR@suppilovahvero>
Date: Thu, 17 Aug 2023 00:00:22 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Roberto Sassu" <roberto.sassu@...weicloud.com>, <corbet@....net>,
<zohar@...ux.ibm.com>, <dmitry.kasatkin@...il.com>,
<paul@...l-moore.com>, <jmorris@...ei.org>, <serge@...lyn.com>
Cc: <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<linux-integrity@...r.kernel.org>,
<linux-security-module@...r.kernel.org>, <bpf@...r.kernel.org>,
<pbrobinson@...il.com>, <zbyszek@...waw.pl>, <hch@....de>,
<mjg59@...f.ucam.org>, <pmatilai@...hat.com>, <jannh@...gle.com>,
"Roberto Sassu" <roberto.sassu@...wei.com>
Subject: Re: [RFC][PATCH v2 03/13] integrity/digest_cache: Add functions to
populate and search
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@...wei.com>
> >>
> >> 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@...wei.com>
> >> ---
> >> 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
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