On 24/07/20, Sumit Garg wrote:
> On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz <jorge@xxxxxxxxxxxx> 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.
>
> I am not sure how this is possible, can you elaborate?
currently, if the user sets max 0, get_optee_rng_data will regardless
issuese a call to the secure world requesting 0 bytes from the RNG
with this patch, this request is avoided.
>
> >
> > Signed-off-by: Jorge Ramirez-Ortiz <jorge@xxxxxxxxxxxx>
> > ---
> > 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))
>
> If read == max, would there be any sleep?
no but I see no reason why there should be a wait since we already have
all the data that we need; the msleep is only required when we need to
wait for the RNG to generate entropy for the number of bytes we are
requesting. if we are requesting 0 bytes, the entropy is already
available. at leat this is what makes sense to me.
>
> -Sumit
>
> > return read;
> > msleep((1000 * (max - read)) / pvt_data->data_rate);
> > } else {
> > --
> > 2.17.1
> >
