From mboxrd@z Thu Jan 1 00:00:00 1970 From: Herbert Xu Subject: Re: [PATCH] omap-rng: Change RNG_CONFIG_REG to RNG_CONTROL_REG when checking and disabling TRNG Date: Tue, 17 Mar 2015 22:33:09 +1100 Message-ID: <20150317113309.GA12224@gondor.apana.org.au> References: <1426461551-14130-1-git-send-email-Andre.Wolokita@analog.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-crypto@vger.kernel.org To: Andre Wolokita Return-path: Received: from ringil.hengli.com.au ([178.18.16.133]:33502 "EHLO ringil.hengli.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753246AbbCQLdR (ORCPT ); Tue, 17 Mar 2015 07:33:17 -0400 Content-Disposition: inline In-Reply-To: <1426461551-14130-1-git-send-email-Andre.Wolokita@analog.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On Mon, Mar 16, 2015 at 10:19:11AM +1100, Andre Wolokita wrote: > In omap4_rng_init(), a check of bit 10 of the RNG_CONFIG_REG is done to determine > whether the RNG is running. This is suspicious firstly due to the use of > RNG_CONTROL_ENABLE_TRNG_MASK and secondly because the same mask is written to > RNG_CONTROL_REG after configuration of the FROs. Similar suspicious logic is > repeated in omap4_rng_cleanup() when RNG_CONTROL_REG masked with > RNG_CONTROL_ENABLE_TRNG_MASK is read, the same mask bit is cleared, and then > written to RNG_CONFIG_REG. Unless the TRNG is enabled with one bit in RNG_CONTROL > and disabled with another in RNG_CONFIG and these bits are mirrored in some way, > I believe that the TRNG is not really shutting off. > > Apart from the strange logic, I have reason to suspect that the OMAP4 related > code in this driver is driving an Inside Secure IP hardware RNG and strongly > suspect that bit 10 of RNG_CONFIG_REG is one of the bits configuring the > sampling rate of the FROs. This option is by default set to 0 and is not being > set anywhere in omap-rng.c. Reading this bit during omap4_rng_init() will > always return 0. It will remain 0 because ~(value of TRNG_MASK in control) will > always be 0, because the TRNG is never shut off. This is of course presuming > that the OMAP4 features the Inside Secure IP. > > I'm interested in knowing what the guys at TI think about this, as only they > can confirm or deny the detailed structure of these registers. > > Signed-off-by: Andre Wolokita Both patches applied. Thanks! -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt