Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751182AbaGGElx (ORCPT ); Mon, 7 Jul 2014 00:41:53 -0400 Received: from mail-oa0-f48.google.com ([209.85.219.48]:62935 "EHLO mail-oa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750714AbaGGEls (ORCPT ); Mon, 7 Jul 2014 00:41:48 -0400 MIME-Version: 1.0 In-Reply-To: <515a12ecc5fca5452bf0bfda4d54546d8fb5829c.1404538109.git.amit.shah@redhat.com> References: <515a12ecc5fca5452bf0bfda4d54546d8fb5829c.1404538109.git.amit.shah@redhat.com> Date: Sun, 6 Jul 2014 21:41:47 -0700 X-Google-Sender-Auth: 4ZzAsmChHhZMhZjeXAYGddOIbpw Message-ID: Subject: Re: [PATCH v2 1/2] hwrng: fetch randomness only after device init From: Kees Cook To: Amit Shah Cc: LKML , Virtualization List , Rusty Russell , Herbert Xu , Jason Cooper , "# 3.4.x" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 4, 2014 at 10:34 PM, 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. 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. Reviewed-by: Kees Cook -Kees > > CC: Kees Cook > CC: Jason Cooper > CC: Herbert Xu > CC: # For v3.15+ > Signed-off-by: Amit Shah > --- > drivers/char/hw_random/core.c | 31 +++++++++++++++++++++++++------ > 1 file changed, 25 insertions(+), 6 deletions(-) > > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c > index 334601c..df95e2f 100644 > --- a/drivers/char/hw_random/core.c > +++ b/drivers/char/hw_random/core.c > @@ -55,16 +55,37 @@ static DEFINE_MUTEX(rng_mutex); > static int data_avail; > static u8 *rng_buffer; > > +static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, > + int wait); > + > static size_t rng_buffer_size(void) > { > return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES; > } > > +static void add_early_randomness(struct hwrng *rng) > +{ > + unsigned char bytes[16]; > + int bytes_read; > + > + bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1); > + if (bytes_read > 0) > + add_device_randomness(bytes, bytes_read); > +} > + > static inline int hwrng_init(struct hwrng *rng) > { > + int ret; > + > if (!rng->init) > return 0; > - return rng->init(rng); > + > + ret = rng->init(rng); > + if (ret) > + return ret; > + > + add_early_randomness(rng); > + return ret; > } > > static inline void hwrng_cleanup(struct hwrng *rng) > @@ -304,8 +325,6 @@ int hwrng_register(struct hwrng *rng) > { > 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)) > @@ -347,9 +366,9 @@ 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); > + if (!rng->init) > + add_early_randomness(rng); > + > out_unlock: > mutex_unlock(&rng_mutex); > out: > -- > 1.9.3 > -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/