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keys: Cache the hash value to avoid lots of recalculation

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Cache the hash of the key's type and description in the index key so that
we're not recalculating it every time we look at a key during a search.
The hash function does a bunch of multiplications, so evading those is
probably worthwhile - especially as this is done for every key examined
during a search.

This also allows the methods used by assoc_array to get chunks of index-key
to be simplified.

Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
David Howells 2019-06-26 21:02:32 +01:00
parent f771fde820
commit 355ef8e158
4 changed files with 25 additions and 16 deletions
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3
include/linux/key.h
View File

@ -86,6 +86,8 @@ struct keyring_list;
struct keyring_name;
struct keyring_index_key {
/* [!] If this structure is altered, the union in struct key must change too! */
unsigned long hash; /* Hash value */
union {
struct {
#ifdef __LITTLE_ENDIAN /* Put desc_len at the LSB of x */
@ -213,6 +215,7 @@ struct key {
union {
struct keyring_index_key index_key;
struct {
unsigned long hash;
unsigned long len_desc;
struct key_type *type; /* type of key */
char *description;

8
security/keys/internal.h
View File

@ -89,13 +89,7 @@ extern spinlock_t key_serial_lock;
extern struct mutex key_construction_mutex;
extern wait_queue_head_t request_key_conswq;
static inline void key_set_index_key(struct keyring_index_key *index_key)
{
size_t n = min_t(size_t, index_key->desc_len, sizeof(index_key->desc));
memcpy(index_key->desc, index_key->description, n);
}
extern void key_set_index_key(struct keyring_index_key *index_key);
extern struct key_type *key_type_lookup(const char *type);
extern void key_type_put(struct key_type *ktype);

2
security/keys/key.c
View File

@ -285,12 +285,12 @@ struct key *key_alloc(struct key_type *type, const char *desc,
key->index_key.description = kmemdup(desc, desclen + 1, GFP_KERNEL);
if (!key->index_key.description)
goto no_memory_3;
key->index_key.type = type;
key_set_index_key(&key->index_key);
refcount_set(&key->usage, 1);
init_rwsem(&key->sem);
lockdep_set_class(&key->sem, &type->lock_class);
key->index_key.type = type;
key->user = user;
key->quotalen = quotalen;
key->datalen = type->def_datalen;

28
security/keys/keyring.c
View File

@ -168,7 +168,7 @@ static u64 mult_64x32_and_fold(u64 x, u32 y)
/*
* Hash a key type and description.
*/
static unsigned long hash_key_type_and_desc(const struct keyring_index_key *index_key)
static void hash_key_type_and_desc(struct keyring_index_key *index_key)
{
const unsigned level_shift = ASSOC_ARRAY_LEVEL_STEP;
const unsigned long fan_mask = ASSOC_ARRAY_FAN_MASK;
@ -206,10 +206,22 @@ static unsigned long hash_key_type_and_desc(const struct keyring_index_key *inde
* zero for keyrings and non-zero otherwise.
*/
if (index_key->type != &key_type_keyring && (hash & fan_mask) == 0)
return hash | (hash >> (ASSOC_ARRAY_KEY_CHUNK_SIZE - level_shift)) | 1;
if (index_key->type == &key_type_keyring && (hash & fan_mask) != 0)
return (hash + (hash << level_shift)) & ~fan_mask;
return hash;
hash |= (hash >> (ASSOC_ARRAY_KEY_CHUNK_SIZE - level_shift)) | 1;
else if (index_key->type == &key_type_keyring && (hash & fan_mask) != 0)
hash = (hash + (hash << level_shift)) & ~fan_mask;
index_key->hash = hash;
}
/*
* Finalise an index key to include a part of the description actually in the
* index key and to add in the hash too.
*/
void key_set_index_key(struct keyring_index_key *index_key)
{
size_t n = min_t(size_t, index_key->desc_len, sizeof(index_key->desc));
memcpy(index_key->desc, index_key->description, n);
hash_key_type_and_desc(index_key);
}
/*
@ -227,7 +239,7 @@ static unsigned long keyring_get_key_chunk(const void *data, int level)
level /= ASSOC_ARRAY_KEY_CHUNK_SIZE;
switch (level) {
case 0:
return hash_key_type_and_desc(index_key);
return index_key->hash;
case 1:
return index_key->x;
case 2:
@ -280,8 +292,8 @@ static int keyring_diff_objects(const void *object, const void *data)
int level, i;
level = 0;
seg_a = hash_key_type_and_desc(a);
seg_b = hash_key_type_and_desc(b);
seg_a = a->hash;
seg_b = b->hash;
if ((seg_a ^ seg_b) != 0)
goto differ;
level += ASSOC_ARRAY_KEY_CHUNK_SIZE / 8;