On (Mon) 07 Jul 2014 [11:34:58], Amit Shah wrote:
> On (Mon) 07 Jul 2014 [11:23:52], Amit Shah wrote:
> > On (Sun) 06 Jul 2014 [21:41:47], Kees Cook wrote:
> > > On Fri, Jul 4, 2014 at 10:34 PM, Amit Shah <amit.shah@xxxxxxxxxx> wrote:
> > > > Commit d9e7972619334 "hwrng: add randomness to system from rng sources"
> > > > added a call to rng_get_data() from the hwrng_register() function.
> > > > However, some rng devices need initialization before data can be read
> > > > from them.
> > > >
> > > > This commit makes the call to rng_get_data() depend on no init fn
> > > > pointer being registered by the device. If an init function is
> > > > registered, this call is made after device init.
> > >
> > > Thanks, this seems pretty reasonable. One side-effect is that cycling
> > > between hwrngs via sysfs (when they have init functions) will cause
> > > them to add more entropy. I don't think this is a problem, but it is
> > > kind of a weird side-effect.
> >
> > Yes, agreed. Having a per-device bool that indicates whether the
> > initial randomness is obtained is quite a heavy solution for this
> > side-effect. But I can put this in the commit log so it's clear..
>
> Well actually this feels a little weird, so how about making this the
> default behaviour for all devices, whether they have ->init() or not?
>
> This also means that if a virtio-rng device is switched, it can
> contribute as its probe would have been over.
Something like this - untested:
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 50f5b76..c4419ea 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -81,17 +81,15 @@ static void add_early_randomness(struct hwrng *rng)
static inline int hwrng_init(struct hwrng *rng)
{
- int ret;
-
- if (!rng->init)
- return 0;
-
- ret = rng->init(rng);
- if (ret)
- return ret;
+ if (rng->init) {
+ int ret;
+ ret = rng->init(rng);
+ if (ret)
+ return ret;
+ }
add_early_randomness(rng);
- return ret;
+ return 0;
}
static inline void hwrng_cleanup(struct hwrng *rng)
@@ -372,8 +370,16 @@ int hwrng_register(struct hwrng *rng)
INIT_LIST_HEAD(&rng->list);
list_add_tail(&rng->list, &rng_list);
- if (!rng->init)
+ if (old_rng && !rng->init) {
+ /*
+ * Use a new device's input to add some randomness to
+ * the system. If this rng device isn't going to be
+ * used right away, its init function hasn't been
+ * called yet; so only use the randomness from devices
+ * that don't need an init callback.
+ */
add_early_randomness(rng);
+ }
out_unlock:
mutex_unlock(&rng_mutex);
Amit
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