Re: [PATCH 3/6] crypto: jz4780-rng: Add Ingenic JZ4780 hardware PRNG driver

[Stephan Mueller <smueller@chronox.de>]

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