Re: [PATCH V2] crypto: qcom-rng - Add hw_random interface support

[Om Prakash Singh]

On 9/22/2023 8:46 PM, Bjorn Andersson wrote:
> On Wed, Sep 20, 2023 at 08:34:08AM +0530, Om Prakash Singh wrote:
> > Add hw_random interface support in qcom-rng driver as new IP block
> > in Qualcomm SoC has inbuilt NIST SP800 90B compliant entropic source
> > to generate true random number.
> >
> > Keeping current rng_alg interface as well for random number generation
> > using Kernel Crypto API.
> >
> > Signed-off-by: Om Prakash Singh <quic_omprsing@xxxxxxxxxxx>
> > ---
> >
> > Changes in V2:
> > - Updated patch to fix the return value from qcom_rng_generate() to be
> >    consistent with current implementation
>
> As far as I can tell you didn't change this, see below.
>
> > - Updated patch to make it more concise
> > - Removed unnecessary use local variable and it's initialization
> > - Updated patch to use devm_hwrng_register() instead of hwrng_register()
> > - Updated subject line of the patch
> >
> > This patch is depends on [1]
> > [1] https://lore.kernel.org/lkml/20230824-topic-sm8550-rng-v2-4-dfcafbb16a3e@xxxxxxxxxx/
> >
> >   drivers/crypto/qcom-rng.c | 65 ++++++++++++++++++++++++++++++++++-----
> >   1 file changed, 58 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/crypto/qcom-rng.c b/drivers/crypto/qcom-rng.c
> > index fb54b8cfc35f..e5a574a3cc59 100644
> > --- a/drivers/crypto/qcom-rng.c
> > +++ b/drivers/crypto/qcom-rng.c
> > @@ -7,6 +7,7 @@
> >   #include <linux/acpi.h>
> >   #include <linux/clk.h>
> >   #include <linux/crypto.h>
> > +#include <linux/hw_random.h>
> >   #include <linux/io.h>
> >   #include <linux/iopoll.h>
> >   #include <linux/kernel.h>
> > @@ -32,13 +33,18 @@ struct qcom_rng {
> >   	struct mutex lock;
> >   	void __iomem *base;
> >   	struct clk *clk;
> > -	unsigned int skip_init;
> > +	struct qcom_rng_of_data *of_data;
> >   };
> >   
> >   struct qcom_rng_ctx {
> >   	struct qcom_rng *rng;
> >   };
> >   
> > +struct qcom_rng_of_data {
> > +	bool skip_init;
> > +	bool hwrng_support;
> > +};
> > +
> >   static struct qcom_rng *qcom_rng_dev;
> >   
> >   static int qcom_rng_read(struct qcom_rng *rng, u8 *data, unsigned int max)
> > @@ -70,7 +76,7 @@ static int qcom_rng_read(struct qcom_rng *rng, u8 *data, unsigned int max)
> >   		}
> >   	} while (currsize < max);
> >   
> > -	return 0;
> > +	return currsize;
>
> As I pointed out in my previous review, if the qcom_rng_read() is
> requested to read a number of bytes (max) that is not evenly divisible
> with 4 (WORD_SZ) the loop will exit without accounting for the last
> bytes copied...

I will update implementation to account currsize for accounting 
remaining bytes

> >   }
> >   
> >   static int qcom_rng_generate(struct crypto_rng *tfm,
> > @@ -92,6 +98,9 @@ static int qcom_rng_generate(struct crypto_rng *tfm,
> >   	mutex_unlock(&rng->lock);
> >   	clk_disable_unprepare(rng->clk);
> >   
> > +	if (ret == dlen)
>
> ...this means that if dlen % 4, you're changing the return value of this
> function from 0 to dlen.

I will Update logic for success case return value.

> > +		ret = 0;
> > +
> >   	return ret;
> >   }
> >   
> > @@ -101,6 +110,13 @@ static int qcom_rng_seed(struct crypto_rng *tfm, const u8 *seed,
> >   	return 0;
> >   }
> >   
> > +static int qcom_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> > +{
> > +	struct qcom_rng *qrng = (struct qcom_rng *)rng->priv;
>
> You missed Herbert's request in [1], which I presume implies that
> qcom_hwrng should be moved into struct qcom_rng, which would mean that
> you can get the qrng by container_of().
>
> [1] https://lore.kernel.org/lkml/ZQQvlXvGy8p01uJS@xxxxxxxxxxxxxxxxxxx/

I will address this comment is my next patch set V3.


> > +
> > +	return qcom_rng_read(qrng, data, max);
> > +}
> > +
> >   static int qcom_rng_enable(struct qcom_rng *rng)
> >   {
> >   	u32 val;
> > @@ -136,7 +152,7 @@ static int qcom_rng_init(struct crypto_tfm *tfm)
> >   
> >   	ctx->rng = qcom_rng_dev;
> >   
> > -	if (!ctx->rng->skip_init)
> > +	if (!ctx->rng->of_data->skip_init)
> >   		return qcom_rng_enable(ctx->rng);
> >   
> >   	return 0;
> > @@ -157,6 +173,12 @@ static struct rng_alg qcom_rng_alg = {
> >   	}
> >   };
> >   
> > +static struct hwrng qcom_hwrng = {
> > +	.name = "qcom-hwrng",
> > +	.read = qcom_hwrng_read,
> > +	.quality = 1024,
> > +};
>
> Which would mean not adding this static global variable...
>
> Regards,
> Bjorn