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hwrng: use rng source with best quality

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This patch rewoks the hwrng to always use the
rng source with best entropy quality.

On registation and unregistration the hwrng now
tries to choose the best (= highest quality value)
rng source. The handling of the internal list
of registered rng sources is now always sorted
by quality and the top most rng chosen.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Reviewed-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Harald Freudenberger 2017-07-11 09:36:22 +02:00 committed by Herbert Xu
parent ad818080f6
commit 2bbb698388
1 changed files with 19 additions and 6 deletions
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25
drivers/char/hw_random/core.c
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@ -29,6 +29,7 @@
static struct hwrng *current_rng;
static struct task_struct *hwrng_fill;
/* list of registered rngs, sorted decending by quality */
static LIST_HEAD(rng_list);
/* Protects rng_list and current_rng */
static DEFINE_MUTEX(rng_mutex);
@ -417,6 +418,7 @@ int hwrng_register(struct hwrng *rng)
{
int err = -EINVAL;
struct hwrng *old_rng, *tmp;
struct list_head *rng_list_ptr;
if (!rng->name || (!rng->data_read && !rng->read))
goto out;
@ -432,14 +434,25 @@ int hwrng_register(struct hwrng *rng)
init_completion(&rng->cleanup_done);
complete(&rng->cleanup_done);
/* rng_list is sorted by decreasing quality */
list_for_each(rng_list_ptr, &rng_list) {
tmp = list_entry(rng_list_ptr, struct hwrng, list);
if (tmp->quality < rng->quality)
break;
}
list_add_tail(&rng->list, rng_list_ptr);
old_rng = current_rng;
err = 0;
if (!old_rng) {
if (!old_rng || (rng->quality > old_rng->quality)) {
/*
* Set new rng as current as the new rng source
* provides better entropy quality.
*/
err = set_current_rng(rng);
if (err)
goto out_unlock;
}
list_add_tail(&rng->list, &rng_list);
if (old_rng && !rng->init) {
/*
@ -466,12 +479,12 @@ void hwrng_unregister(struct hwrng *rng)
list_del(&rng->list);
if (current_rng == rng) {
drop_current_rng();
/* rng_list is sorted by quality, use the best (=first) one */
if (!list_empty(&rng_list)) {
struct hwrng *tail;
struct hwrng *new_rng;
tail = list_entry(rng_list.prev, struct hwrng, list);
set_current_rng(tail);
new_rng = list_entry(rng_list.next, struct hwrng, list);
set_current_rng(new_rng);
}
}