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ima: Replace static htable queue with dynamically allocated array

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The IMA hash table is a fixed-size array of hlist_head buckets:

    struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE];

IMA_MEASURE_HTABLE_SIZE is (1 << IMA_HASH_BITS) = 1024 buckets, each a
struct hlist_head (one pointer, 8 bytes on 64-bit). That is 8 KiB allocated
in BSS for every kernel, regardless of whether IMA is ever used, and
regardless of how many measurements are actually made.

Replace the fixed-size array with a RCU-protected pointer to a dynamically
allocated array that is initialized in ima_init_htable(), which is called
from ima_init() during early boot. ima_init_htable() calls the static
function ima_alloc_replace_htable() which, other than initializing the hash
table the first time, can also hot-swap the existing hash table with a
blank one.

The allocation in ima_alloc_replace_htable() uses kcalloc() so the buckets
are zero-initialised (equivalent to HLIST_HEAD_INIT { .first = NULL }).
Callers of ima_alloc_replace_htable() must call synchronize_rcu() and free
the returned hash table.

Finally, access the hash table with rcu_dereference() in
ima_lookup_digest_entry() (reader side) and with
rcu_dereference_protected() in ima_add_digest_entry() (writer side).

No functional change: bucket count, hash function, and all locking remain
identical.

Link: https://github.com/linux-integrity/linux/issues/1
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Roberto Sassu
2026-06-05 19:22:26 +02:00
committed by Mimi Zohar
parent a01183bd6f
commit 7bc01800a7
3 changed files with 50 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
security/integrity/ima/ima.h
View File

@@ -311,6 +311,7 @@ bool ima_template_has_modsig(const struct ima_template_desc *ima_template);
int ima_restore_measurement_entry(struct ima_template_entry *entry);
int ima_restore_measurement_list(loff_t bufsize, void *buf);
int ima_measurements_show(struct seq_file *m, void *v);
int __init ima_init_htable(void);
unsigned long ima_get_binary_runtime_size(void);
int ima_init_template(void);
void ima_init_template_list(void);
@@ -328,7 +329,7 @@ extern spinlock_t ima_queue_lock;
extern atomic_long_t ima_num_records;
/* Total number of violations since hard boot. */
extern atomic_long_t ima_num_violations;
extern struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE];
extern struct hlist_head __rcu *ima_htable;
static inline unsigned int ima_hash_key(u8 *digest)
{

5
security/integrity/ima/ima_init.c
View File

@@ -140,6 +140,11 @@ int __init ima_init(void)
rc = ima_init_digests();
if (rc != 0)
return rc;
rc = ima_init_htable();
if (rc != 0)
return rc;
rc = ima_add_boot_aggregate(); /* boot aggregate must be first entry */
if (rc != 0)
return rc;

48
security/integrity/ima/ima_queue.c
View File

@@ -36,9 +36,7 @@ atomic_long_t ima_num_records = ATOMIC_LONG_INIT(0);
atomic_long_t ima_num_violations = ATOMIC_LONG_INIT(0);
/* key: inode (before secure-hashing a file) */
struct hlist_head ima_htable[IMA_MEASURE_HTABLE_SIZE] = {
[0 ... IMA_MEASURE_HTABLE_SIZE - 1] = HLIST_HEAD_INIT
};
struct hlist_head __rcu *ima_htable;
/* mutex protects atomicity of extending measurement list
* and extending the TPM PCR aggregate. Since tpm_extend can take
@@ -52,17 +50,53 @@ static DEFINE_MUTEX(ima_extend_list_mutex);
*/
static bool ima_measurements_suspended;
/* Callers must call synchronize_rcu() and free the hash table. */
static struct hlist_head *ima_alloc_replace_htable(void)
{
struct hlist_head *old_htable, *new_htable;
/* Initializing to zeros is equivalent to call HLIST_HEAD_INIT. */
new_htable = kcalloc(IMA_MEASURE_HTABLE_SIZE, sizeof(struct hlist_head),
GFP_KERNEL);
if (!new_htable)
return ERR_PTR(-ENOMEM);
old_htable = rcu_replace_pointer(ima_htable, new_htable,
lockdep_is_held(&ima_extend_list_mutex));
return old_htable;
}
int __init ima_init_htable(void)
{
struct hlist_head *old_htable;
mutex_lock(&ima_extend_list_mutex);
old_htable = ima_alloc_replace_htable();
mutex_unlock(&ima_extend_list_mutex);
if (IS_ERR(old_htable))
return PTR_ERR(old_htable);
/* Synchronize_rcu() and kfree() not necessary, only for robustness. */
synchronize_rcu();
kfree(old_htable);
return 0;
}
/* lookup up the digest value in the hash table, and return the entry */
static struct ima_queue_entry *ima_lookup_digest_entry(u8 *digest_value,
int pcr)
{
struct ima_queue_entry *qe, *ret = NULL;
struct hlist_head *htable;
unsigned int key;
int rc;
key = ima_hash_key(digest_value);
rcu_read_lock();
hlist_for_each_entry_rcu(qe, &ima_htable[key], hnext) {
htable = rcu_dereference(ima_htable);
hlist_for_each_entry_rcu(qe, &htable[key], hnext) {
rc = memcmp(qe->entry->digests[ima_hash_algo_idx].digest,
digest_value, hash_digest_size[ima_hash_algo]);
if ((rc == 0) && (qe->entry->pcr == pcr)) {
@@ -102,6 +136,7 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
bool update_htable)
{
struct ima_queue_entry *qe;
struct hlist_head *htable;
unsigned int key;
qe = kmalloc_obj(*qe);
@@ -114,10 +149,13 @@ static int ima_add_digest_entry(struct ima_template_entry *entry,
INIT_LIST_HEAD(&qe->later);
list_add_tail_rcu(&qe->later, &ima_measurements);
htable = rcu_dereference_protected(ima_htable,
lockdep_is_held(&ima_extend_list_mutex));
atomic_long_inc(&ima_num_records);
if (update_htable) {
key = ima_hash_key(entry->digests[ima_hash_algo_idx].digest);
hlist_add_head_rcu(&qe->hnext, &ima_htable[key]);
hlist_add_head_rcu(&qe->hnext, &htable[key]);
}
if (binary_runtime_size != ULONG_MAX) {