linux-kernel - Re: [PATCHv2 2/2] hwrng: optee: fix wait use case

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Date:   Wed, 5 Aug 2020 15:34:20 +0200
From:   "Jorge Ramirez-Ortiz, Foundries" <jorge@...ndries.io>
To:     Jorge Ramirez-Ortiz <jorge@...ndries.io>
Cc:     sumit.garg@...aro.org, mpm@...enic.com,
        herbert@...dor.apana.org.au, jens.wiklander@...aro.org,
        arnd@...db.de, ricardo@...ndries.io, mike@...ndries.io,
        gregkh@...uxfoundation.org, op-tee@...ts.trustedfirmware.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 2/2] hwrng: optee: fix wait use case

On 23/07/20, Jorge Ramirez-Ortiz wrote:
> The current code waits for data to be available before attempting a
> second read. However the second read would not be executed as the
> while loop exits.
> 
> This fix does not wait if all data has been read and reads a second
> time if only partial data was retrieved on the first read.
> 
> This fix also does not attempt to read if not data is requested.
> 
> Signed-off-by: Jorge Ramirez-Ortiz <jorge@...ndries.io>
> ---
>  v2: tidy up the while loop to avoid reading when no data is requested
> 
>  drivers/char/hw_random/optee-rng.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/hw_random/optee-rng.c b/drivers/char/hw_random/optee-rng.c
> index 5bc4700c4dae..a99d82949981 100644
> --- a/drivers/char/hw_random/optee-rng.c
> +++ b/drivers/char/hw_random/optee-rng.c
> @@ -122,14 +122,14 @@ static int optee_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
>  	if (max > MAX_ENTROPY_REQ_SZ)
>  		max = MAX_ENTROPY_REQ_SZ;
>  
> -	while (read == 0) {
> +	while (read < max) {
>  		rng_size = get_optee_rng_data(pvt_data, data, (max - read));
>  
>  		data += rng_size;
>  		read += rng_size;
>  
>  		if (wait && pvt_data->data_rate) {
> -			if (timeout-- == 0)
> +			if ((timeout-- == 0) || (read == max))
>  				return read;
>  			msleep((1000 * (max - read)) / pvt_data->data_rate);
>  		} else {

any comments please?