Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751841AbaGGGka (ORCPT ); Mon, 7 Jul 2014 02:40:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57741 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751163AbaGGGk0 (ORCPT ); Mon, 7 Jul 2014 02:40:26 -0400 Date: Mon, 7 Jul 2014 12:09:56 +0530 From: Amit Shah To: Kees Cook Cc: LKML , Virtualization List , Rusty Russell , Herbert Xu , Jason Cooper , "# 3.4.x" Subject: Re: [PATCH v2 1/2] hwrng: fetch randomness only after device init Message-ID: <20140707063956.GE27024@grmbl.mre> References: <515a12ecc5fca5452bf0bfda4d54546d8fb5829c.1404538109.git.amit.shah@redhat.com> <20140707055352.GB27024@grmbl.mre> <20140707060458.GC27024@grmbl.mre> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140707060458.GC27024@grmbl.mre> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 -- 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/