[RFC PATCH] hwrng: sysfs entry rng_seed_kernel, was: "Re: [PATCH v2 1/2] hwrng: fetch randomness only after device init"
From: Jason Cooper
Date: Wed Jul 09 2014 - 12:07:39 EST
Amit, Kees,
On Wed, Jul 09, 2014 at 06:55:24PM +0530, Amit Shah wrote:
> On (Wed) 09 Jul 2014 [09:17:37], Jason Cooper wrote:
> > On Wed, Jul 09, 2014 at 06:38:22PM +0530, Amit Shah wrote:
> > > On (Wed) 09 Jul 2014 [07:53:17], Jason Cooper wrote:
> > > > On Sat, Jul 05, 2014 at 11:04:52AM +0530, Amit Shah 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.
> > > > >
> > > > > CC: Kees Cook <keescook@xxxxxxxxxxxx>
> > > > > CC: Jason Cooper <jason@xxxxxxxxxxxxxx>
> > > > > CC: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > > > > CC: <stable@xxxxxxxxxxxxxxx> # For v3.15+
> > > > > Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
> > > > > ---
> > > > > drivers/char/hw_random/core.c | 31 +++++++++++++++++++++++++------
> > > > > 1 file changed, 25 insertions(+), 6 deletions(-)
> > > >
> > > > Thanks for cleaning this up!
> > >
> > > Thanks!
> > >
> > > Any thoughts on the follow-up patch posted later that resolves some of
> > > the weirdness in init?
> >
> > hmm, I'd rather see an init function for virtio-rng that checks the bit
> > and returns 0 or -EAGAIN. With your proposed change, you would get
> > hangs again.
>
> Confused; I meant the patch in
>
> https://lkml.org/lkml/2014/7/7/58
Yes, I meant without 2/2 of this current series.
I'm cooling to the idea of the init function for virtio-rng, and it
might be best just to admit that there's no way to seed the entropy pool
from the virtio-rng at probe time. After all, once userspace is up, the
system should take advantage of /dev/hwrng for the generation of
long-term keys. Either via rngd feeding /dev/random, or directly.
As for the follow-on patch you asked about, I think that's fine. More
entropy can't hurt.
The below patch might be worth considering so that the user of a system
with only virtio-rng can kick the entropy pool as they see fit. It's
probably not too kosher as is, but if the idea is liked, I could clean
it up and submit.
The advantage is that users don't need to have rngd installed and
running on the system in order to jump-start the entropy pool.
thx,
Jason.
------------>8----------------
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index df95e2ff9d48..b54af066d075 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -63,14 +63,25 @@ static size_t rng_buffer_size(void)
return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
}
-static void add_early_randomness(struct hwrng *rng)
+static void add_early_randomness(struct hwrng *rng, u8 size)
{
- unsigned char bytes[16];
+ unsigned char *bytes;
int bytes_read;
+ /* size can come from the user, sanitize */
+ size = size > 256 ? 256 : size;
+
+ size = size == 0 ? 16 : size;
+
+ bytes = kmalloc(size, GFP_KERNEL);
+ if (!bytes)
+ return;
+
bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
if (bytes_read > 0)
add_device_randomness(bytes, bytes_read);
+
+ kfree(bytes);
}
static inline int hwrng_init(struct hwrng *rng)
@@ -84,7 +95,7 @@ static inline int hwrng_init(struct hwrng *rng)
if (ret)
return ret;
- add_early_randomness(rng);
+ add_early_randomness(rng, 0);
return ret;
}
@@ -281,18 +292,54 @@ static ssize_t hwrng_attr_available_show(struct device *dev,
return ret;
}
+/*
+ * seed the kernel's entropy pool from the current hwrng.
+ *
+ * 'echo "n" >rng_seed_kernel', where n >= 0.
+ * n = 0: default size added (16 bytes)
+ * 0 < n <= 256: n bytes added.
+ * n > 256: 256 bytes added.
+ */
+static ssize_t hwrng_attr_seed_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t len)
+{
+ int err;
+ u8 sz;
+
+ if (!current_rng)
+ return -ENODEV;
+
+ err = kstrtou8(buf, 10, &sz);
+ if (err)
+ return err;
+
+ err = mutex_lock_interruptible(&rng_mutex);
+ if (err)
+ return -ERESTARTSYS;
+
+ add_early_randomness(current_rng, sz);
+
+ mutex_unlock(&rng_mutex);
+
+ return err ? : len;
+}
+
static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
hwrng_attr_current_show,
hwrng_attr_current_store);
static DEVICE_ATTR(rng_available, S_IRUGO,
hwrng_attr_available_show,
NULL);
-
+static DEVICE_ATTR(rng_seed_kernel, S_IWUSR,
+ NULL,
+ hwrng_attr_seed_store);
static void unregister_miscdev(void)
{
device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
+ device_remove_file(rng_miscdev.this_device, &dev_attr_rng_seed_kernel);
misc_deregister(&rng_miscdev);
}
@@ -311,9 +358,15 @@ static int register_miscdev(void)
&dev_attr_rng_available);
if (err)
goto err_remove_current;
+ err = device_create_file(rng_miscdev.this_device,
+ &dev_attr_rng_seed_kernel);
+ if (err)
+ goto err_remove_available;
out:
return err;
+err_remove_available:
+ device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
err_remove_current:
device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
err_misc_dereg:
@@ -367,7 +420,7 @@ int hwrng_register(struct hwrng *rng)
list_add_tail(&rng->list, &rng_list);
if (!rng->init)
- add_early_randomness(rng);
+ add_early_randomness(rng, 0);
out_unlock:
mutex_unlock(&rng_mutex);
--
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