static int
makeprng(void)
{
/* can't create in cprng_init(), too early */
sysctl_prng = cprng_strong_create("sysctl", IPL_NONE,
CPRNG_INIT_ANY|CPRNG_REKEY_ANY);
return 0;
}
/*
* Fetch a per-CPU CPRNG, or create and save one if necessary.
*/
static struct cprng_strong *
rnd_percpu_cprng(void)
{
struct cprng_strong **cprngp, *cprng, *tmp = NULL;
/* Fast path: if there already is a CPRNG for this CPU, use it. */
cprngp = percpu_getref(percpu_urandom_cprng);
cprng = *cprngp;
if (__predict_true(cprng != NULL))
goto out;
percpu_putref(percpu_urandom_cprng);
/*
* Slow path: create a CPRNG named by this CPU.
*
* XXX The CPU of the name may be different from the CPU to
* which it is assigned, because we need to choose a name and
* allocate a cprng while preemption is enabled. This could be
* fixed by changing the cprng_strong API (e.g., by adding a
* cprng_strong_setname or by separating allocation from
* initialization), but it's not clear that's worth the
* trouble.
*/
char name[32];
(void)snprintf(name, sizeof(name), "urandom%u", cpu_index(curcpu()));
tmp = cprng_strong_create(name, IPL_NONE,
(CPRNG_INIT_ANY | CPRNG_REKEY_ANY));
/* Try again, but we may have been preempted and lost a race. */
cprngp = percpu_getref(percpu_urandom_cprng);
cprng = *cprngp;
if (__predict_false(cprng != NULL))
goto out;
/* Commit the CPRNG we just created. */
cprng = tmp;
tmp = NULL;
*cprngp = cprng;
out: percpu_putref(percpu_urandom_cprng);
if (tmp != NULL)
cprng_strong_destroy(tmp);
KASSERT(cprng != NULL);
return cprng;
}
/*
* Fetch a /dev/u?random context's CPRNG, or create and save one if
* necessary.
*/
static struct cprng_strong *
rnd_ctx_cprng(struct rnd_ctx *ctx)
{
struct cprng_strong *cprng, *tmp = NULL;
/* Fast path: if someone has already allocated a CPRNG, use it. */
cprng = ctx->rc_cprng;
if (__predict_true(cprng != NULL)) {
/* Make sure the CPU hasn't prefetched cprng's guts. */
membar_consumer();
goto out;
}
/* Slow path: create a CPRNG. Allocate before taking locks. */
char name[64];
struct lwp *const l = curlwp;
(void)snprintf(name, sizeof(name), "%d %"PRIu64" %u",
(int)l->l_proc->p_pid, l->l_ncsw, l->l_cpticks);
const int flags = (ctx->rc_hard? (CPRNG_USE_CV | CPRNG_HARD) :
(CPRNG_INIT_ANY | CPRNG_REKEY_ANY));
tmp = cprng_strong_create(name, IPL_NONE, flags);
/* Publish cprng's guts before the pointer to them. */
membar_producer();
/* Attempt to publish tmp, unless someone beat us. */
cprng = atomic_cas_ptr(&ctx->rc_cprng, NULL, tmp);
if (__predict_false(cprng != NULL)) {
/* Make sure the CPU hasn't prefetched cprng's guts. */
membar_consumer();
goto out;
}
/* Published. Commit tmp. */
cprng = tmp;
tmp = NULL;
out: if (tmp != NULL)
cprng_strong_destroy(tmp);
KASSERT(cprng != NULL);
return cprng;
}
