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

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Hi Stephan,

On 18 August 2017 at 00:22, Stephan Mueller <smueller@xxxxxxxxxx> wrote:
> 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.

You are right. I initially used hw_random framework for this driver.
But later realised that PRNG driver should use crypto framework. When
I started using crypto I reused most of the code. This was because of
porting. Will change it and send next version.

>
>> +             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

Thanks,
PrasannaKumar



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