The creation of a shadow copy is intended to only hold a short term
lock. But the drawback is that parallel users have a very similar DRBG
state which only differs by a high-resolution time stamp.
As the locking is changed to use a long-term lock to avoid such similar
DRBG states, the entire creation and maintenance of a shadow copy can be
removed.
Signed-off-by: Stephan Mueller <smuel...@chronox.de>
---
crypto/drbg.c | 122 ++++++----------------------------------------------------
1 file changed, 11 insertions(+), 111 deletions(-)
diff --git a/crypto/drbg.c b/crypto/drbg.c
index 8d2944f..c8a083c 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -1189,79 +1189,6 @@ err:
return ret;
}
-/*
- * Strategy to avoid holding long term locks: generate a shadow copy of DRBG
- * and perform all operations on this shadow copy. After finishing, restore
- * the updated state of the shadow copy into original drbg state. This way,
- * only the read and write operations of the original drbg state must be
- * locked
- */
-static inline void drbg_copy_drbg(struct drbg_state *src,
- struct drbg_state *dst)
-{
- if (!src || !dst)
- return;
- memcpy(dst->V, src->V, drbg_statelen(src));
- memcpy(dst->C, src->C, drbg_statelen(src));
- dst->reseed_ctr = src->reseed_ctr;
- dst->seeded = src->seeded;
- dst->pr = src->pr;
-#ifdef CONFIG_CRYPTO_FIPS
- dst->fips_primed = src->fips_primed;
- memcpy(dst->prev, src->prev, drbg_blocklen(src));
-#endif
- /*
- * Not copied:
- * scratchpad is initialized drbg_alloc_state;
- * priv_data is initialized with call to crypto_init;
- * d_ops and core are set outside, as these parameters are const;
- * test_data is set outside to prevent it being copied back.
- */
-}
-
-static int drbg_make_shadow(struct drbg_state *drbg, struct drbg_state
**shadow)
-{
- int ret = -ENOMEM;
- struct drbg_state *tmp = NULL;
-
- tmp = kzalloc(sizeof(struct drbg_state), GFP_KERNEL);
- if (!tmp)
- return -ENOMEM;
-
- /* read-only data as they are defined as const, no lock needed */
- tmp->core = drbg->core;
- tmp->d_ops = drbg->d_ops;
-
- ret = drbg_alloc_state(tmp);
- if (ret)
- goto err;
-
- spin_lock_bh(&drbg->drbg_lock);
- drbg_copy_drbg(drbg, tmp);
- /* only make a link to the test buffer, as we only read that data */
- tmp->test_data = drbg->test_data;
- spin_unlock_bh(&drbg->drbg_lock);
- *shadow = tmp;
- return 0;
-
-err:
- kzfree(tmp);
- return ret;
-}
-
-static void drbg_restore_shadow(struct drbg_state *drbg,
- struct drbg_state **shadow)
-{
- struct drbg_state *tmp = *shadow;
-
- spin_lock_bh(&drbg->drbg_lock);
- drbg_copy_drbg(tmp, drbg);
- spin_unlock_bh(&drbg->drbg_lock);
- drbg_dealloc_state(tmp);
- kzfree(tmp);
- *shadow = NULL;
-}
-
/*************************************************************************
* DRBG interface functions
*************************************************************************/
@@ -1287,13 +1214,7 @@ static int drbg_generate(struct drbg_state *drbg,
struct drbg_string *addtl)
{
int len = 0;
- struct drbg_state *shadow = NULL;
LIST_HEAD(addtllist);
- struct drbg_string timestamp;
- union {
- cycles_t cycles;
- unsigned char char_cycles[sizeof(cycles_t)];
- } now;
if (0 == buflen || !buf) {
pr_devel("DRBG: no output buffer provided\n");
@@ -1304,15 +1225,9 @@ static int drbg_generate(struct drbg_state *drbg,
return -EINVAL;
}
- len = drbg_make_shadow(drbg, &shadow);
- if (len) {
- pr_devel("DRBG: shadow copy cannot be generated\n");
- return len;
- }
-
/* 9.3.1 step 2 */
len = -EINVAL;
- if (buflen > (drbg_max_request_bytes(shadow))) {
+ if (buflen > (drbg_max_request_bytes(drbg))) {
pr_devel("DRBG: requested random numbers too large %u\n",
buflen);
goto err;
@@ -1321,7 +1236,7 @@ static int drbg_generate(struct drbg_state *drbg,
/* 9.3.1 step 3 is implicit with the chosen DRBG */
/* 9.3.1 step 4 */
- if (addtl && addtl->len > (drbg_max_addtl(shadow))) {
+ if (addtl && addtl->len > (drbg_max_addtl(drbg))) {
pr_devel("DRBG: additional information string too long %zu\n",
addtl->len);
goto err;
@@ -1332,46 +1247,34 @@ static int drbg_generate(struct drbg_state *drbg,
* 9.3.1 step 6 and 9 supplemented by 9.3.2 step c is implemented
* here. The spec is a bit convoluted here, we make it simpler.
*/
- if ((drbg_max_requests(shadow)) < shadow->reseed_ctr)
- shadow->seeded = false;
+ if ((drbg_max_requests(drbg)) < drbg->reseed_ctr)
+ drbg->seeded = false;
/* allocate cipher handle */
- len = shadow->d_ops->crypto_init(shadow);
+ len = drbg->d_ops->crypto_init(drbg);
if (len)
goto err;
- if (shadow->pr || !shadow->seeded) {
+ if (drbg->pr || !drbg->seeded) {
pr_devel("DRBG: reseeding before generation (prediction "
"resistance: %s, state %s)\n",
drbg->pr ? "true" : "false",
drbg->seeded ? "seeded" : "unseeded");
/* 9.3.1 steps 7.1 through 7.3 */
- len = drbg_seed(shadow, addtl, true);
+ len = drbg_seed(drbg, addtl, true);
if (len)
goto err;
/* 9.3.1 step 7.4 */
addtl = NULL;
}
- /*
- * Mix the time stamp into the DRBG state if the DRBG is not in
- * test mode. If there are two callers invoking the DRBG at the same
- * time, i.e. before the first caller merges its shadow state back,
- * both callers would obtain the same random number stream without
- * changing the state here.
- */
- if (!drbg->test_data) {
- now.cycles = random_get_entropy();
- drbg_string_fill(×tamp, now.char_cycles, sizeof(cycles_t));
- list_add_tail(×tamp.list, &addtllist);
- }
if (addtl && 0 < addtl->len)
list_add_tail(&addtl->list, &addtllist);
/* 9.3.1 step 8 and 10 */
- len = shadow->d_ops->generate(shadow, buf, buflen, &addtllist);
+ len = drbg->d_ops->generate(drbg, buf, buflen, &addtllist);
/* 10.1.1.4 step 6, 10.1.2.5 step 7, 10.2.1.5.2 step 7 */
- shadow->reseed_ctr++;
+ drbg->reseed_ctr++;
if (0 >= len)
goto err;
@@ -1391,7 +1294,7 @@ static int drbg_generate(struct drbg_state *drbg,
* case somebody has a need to implement the test of 11.3.3.
*/
#if 0
- if (shadow->reseed_ctr && !(shadow->reseed_ctr % 4096)) {
+ if (drbg->reseed_ctr && !(drbg->reseed_ctr % 4096)) {
int err = 0;
pr_devel("DRBG: start to perform self test\n");
if (drbg->core->flags & DRBG_HMAC)
@@ -1410,8 +1313,6 @@ static int drbg_generate(struct drbg_state *drbg,
* are returned when reusing this DRBG cipher handle
*/
drbg_uninstantiate(drbg);
- drbg_dealloc_state(shadow);
- kzfree(shadow);
return 0;
} else {
pr_devel("DRBG: self test successful\n");
@@ -1425,8 +1326,7 @@ static int drbg_generate(struct drbg_state *drbg,
*/
len = 0;
err:
- shadow->d_ops->crypto_fini(shadow);
- drbg_restore_shadow(drbg, &shadow);
+ drbg->d_ops->crypto_fini(drbg);
return len;
}
--
2.1.0
--
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