From: Stephan Mueller Subject: Re: [PATCH 3/6] crypto: jz4780-rng: Add Ingenic JZ4780 hardware PRNG driver Date: Thu, 17 Aug 2017 20:52:49 +0200 Message-ID: <20325029.4QLNKKN8OS@tauon.chronox.de> References: <20170817182520.20102-1-prasannatsmkumar@gmail.com> <20170817182520.20102-4-prasannatsmkumar@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: herbert@gondor.apana.org.au, robh+dt@kernel.org, mark.rutland@arm.com, ralf@linux-mips.org, mturquette@baylibre.com, sboyd@codeaurora.org, davem@davemloft.net, paul@crapouillou.net, linux-crypto@vger.kernel.org, linux-mips@linux-mips.org To: PrasannaKumar Muralidharan Return-path: Received: from mail.eperm.de ([89.247.134.16]:58976 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752236AbdHQSwv (ORCPT ); Thu, 17 Aug 2017 14:52:51 -0400 In-Reply-To: <20170817182520.20102-4-prasannatsmkumar@gmail.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: Am Donnerstag, 17. August 2017, 20:25:17 CEST schrieb PrasannaKumar Muralidharan: Hi PrasannaKumar, > + > +static int jz4780_rng_generate(struct crypto_rng *tfm, > + const u8 *src, unsigned int slen, > + u8 *dst, unsigned int dlen) > +{ > + struct jz4780_rng_ctx *ctx = crypto_rng_ctx(tfm); > + struct jz4780_rng *rng = ctx->rng; > + u32 data; > + > + /* > + * JZ4780 Programmers manual says the RNG should not run continuously > + * for more than 1s. So enable RNG, read data and disable it. > + * NOTE: No issue was observed with MIPS creator CI20 board even when > + * RNG ran continuously for longer periods. This is just a precaution. > + * > + * A delay is required so that the current RNG data is not bit shifted > + * version of previous RNG data which could happen if random data is > + * read continuously from this device. > + */ > + jz4780_rng_writel(rng, 1, REG_RNG_CTRL); > + do { > + data = jz4780_rng_readl(rng, REG_RNG_DATA); > + memcpy((void *)dst, (void *)&data, 4); How do you know that dst is a multiple of 4 bytes? When dlen is only 3, you overflow the buffer. > + dlen -= 4; > + dst += 4; > + udelay(20); > + } while (dlen >= 4); > + > + if (dlen > 0) { > + data = jz4780_rng_readl(rng, REG_RNG_DATA); > + memcpy((void *)dst, (void *)&data, dlen); > + } > + jz4780_rng_writel(rng, 0, REG_RNG_CTRL); > + > + return 0; > +} Ciao Stephan