On 24/07/20, Sumit Garg wrote:
On Thu, 23 Jul 2020 at 14:16, Jorge Ramirez-Ortiz jorge@foundries.io 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@foundries.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))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