Re: [PATCH][RESEND 3] hwrng: add randomness to system from rng
sources
[Posted March 12, 2014 by jake]
| From: |
| Jason Cooper <jason-AT-lakedaemon.net> |
| To: |
| Kees Cook <keescook-AT-chromium.org>, Theodore Ts'o <tytso-AT-mit.edu> |
| Subject: |
| Re: [PATCH][RESEND 3] hwrng: add randomness to system from rng sources |
| Date: |
| Tue, 4 Mar 2014 10:38:42 -0500 |
| Message-ID: |
| <20140304153841.GN1872@titan.lakedaemon.net> |
| Cc: |
| linux-kernel-AT-vger.kernel.org, Matt Mackall <mpm-AT-selenic.com>, Herbert Xu <herbert-AT-gondor.apana.org.au>, Rusty Russell <rusty-AT-rustcorp.com.au>, Satoru Takeuchi <satoru.takeuchi-AT-gmail.com>, linux-crypto-AT-vger.kernel.org, Andrew Morton <akpm-AT-linux-foundation.org> |
| Archive‑link: | |
Article |
Kees, Ted,
On Mon, Mar 03, 2014 at 03:51:48PM -0800, Kees Cook wrote:
> When bringing a new RNG source online, it seems like it would make sense
> to use some of its bytes to make the system entropy pool more random,
> as done with all sorts of other devices that contain per-device or
> per-boot differences.
Why is this necessary? init_std_data() already calls
arch_get_random_long() while stirring each of the pools.
I'm a little concerned here because this gives potentially untrusted
hwrngs more influence over the entropy pools initial state than most
users of random.c expect. Many of the drivers in hw_random/ are
platform drivers and are initialized before random.c.
I'm comfortable with the design decisions Ted has made wrt random.c and
hwrngs. However, I think that this changes that trust relationship in a
fundamental way. I'm ok with building support into my kernels for
hwrngs as long as random.c's internal use of them is limited to the
mixing in extract_buf() and init_std_data().
By adding this patch, even without crediting entropy to the pool, a
rogue hwrng now has significantly more influence over the initial state
of the entropy pools. Or, am I missing something?
thx,
Jason.
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> drivers/char/hw_random/core.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index a0f7724852eb..6e5bb68a708c 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -41,6 +41,7 @@
> #include <linux/miscdevice.h>
> #include <linux/delay.h>
> #include <linux/slab.h>
> +#include <linux/random.h>
> #include <asm/uaccess.h>
>
>
> @@ -305,6 +306,8 @@ int hwrng_register(struct hwrng *rng)
> int must_register_misc;
> int err = -EINVAL;
> struct hwrng *old_rng, *tmp;
> + unsigned char bytes[16];
> + int bytes_read;
>
> if (rng->name == NULL ||
> (rng->data_read == NULL && rng->read == NULL))
> @@ -348,6 +351,10 @@ int hwrng_register(struct hwrng *rng)
> }
> INIT_LIST_HEAD(&rng->list);
> list_add_tail(&rng->list, &rng_list);
> +
> + bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> + if (bytes_read > 0)
> + add_device_randomness(bytes, bytes_read);
> out_unlock:
> mutex_unlock(&rng_mutex);
> out:
> --
> 1.7.9.5
>
>
> --
> Kees Cook
> Chrome OS Security
> --
> To unsubscribe from this list: send the line "unsubscribe linux-crypto" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
