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keys: Cache the hash value to avoid lots of recalculation 

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;