Linux-Crypto Archive on lore.kernel.org
 help / color / Atom feed
From: "Jorge Ramirez-Ortiz, Foundries" <jorge@foundries.io>
To: Sumit Garg <sumit.garg@linaro.org>
Cc: "Jorge Ramirez-Ortiz, Foundries" <jorge@foundries.io>,
	Matt Mackall <mpm@selenic.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Jens Wiklander <jens.wiklander@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	ricardo@foundries.io, Michael Scott <mike@foundries.io>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	op-tee@lists.trustedfirmware.org,
	"open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
	<linux-crypto@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCHv2 2/2] hwrng: optee: fix wait use case
Date: Wed, 5 Aug 2020 22:38:17 +0200
Message-ID: <20200805203817.GA12229@trex> (raw)
In-Reply-To: <CAFA6WYOGu4DPzd93h-yFLJvLmRH=ZroN70+ZNY6xCOOM+TJOSA@mail.gmail.com>

On 05/08/20, Sumit Garg wrote:
> Apologies for my delayed response as I was busy with some other tasks
> along with holidays.

no pb! was just making sure this wasnt falling through some cracks.

> 
> On Fri, 24 Jul 2020 at 19:53, Jorge Ramirez-Ortiz, Foundries
> <jorge@foundries.io> wrote:
> >
> > 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
> >
> 
> This case is already handled by core API: rng_dev_read().

ah ok good point, you are right
but yeah, there is no consequence to the actual patch.

> 
> > 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.
> >
> 
> Wouldn't it lead to a call as msleep(0); that means no wait as well?

I dont understand: there is no reason to wait if read == max and this
patch will not wait: if read == max it calls 'return read'

am I misunderstanding your point?

> 
> -Sumit
> 
> >
> > >
> > > -Sumit
> > >
> > > >                                 return read;
> > > >                         msleep((1000 * (max - read)) / pvt_data->data_rate);
> > > >                 } else {
> > > > --
> > > > 2.17.1
> > > >

  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-23  8:46 [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Jorge Ramirez-Ortiz
2020-07-23  8:46 ` [PATCHv2 2/2] hwrng: optee: fix wait use case Jorge Ramirez-Ortiz
2020-07-24 13:22   ` Sumit Garg
2020-07-24 14:23     ` Jorge Ramirez-Ortiz, Foundries
2020-07-28 10:05       ` Jorge Ramirez-Ortiz, Foundries
2020-08-05 13:49       ` Sumit Garg
2020-08-05 20:38         ` Jorge Ramirez-Ortiz, Foundries [this message]
2020-08-06  6:11           ` Sumit Garg
2020-08-06  6:30             ` Jorge Ramirez-Ortiz, Foundries
2020-08-06  6:57               ` Sumit Garg
2020-08-06  8:14                 ` Jorge Ramirez-Ortiz, Foundries
2020-08-06  9:15                   ` Sumit Garg
2020-08-05 13:34   ` Jorge Ramirez-Ortiz, Foundries
2020-07-24 13:24 ` [PATCHv2 1/2] hwrng: optee: handle unlimited data rates Sumit Garg

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200805203817.GA12229@trex \
    --to=jorge@foundries.io \
    --cc=arnd@arndb.de \
    --cc=gregkh@linuxfoundation.org \
    --cc=herbert@gondor.apana.org.au \
    --cc=jens.wiklander@linaro.org \
    --cc=linux-crypto@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mike@foundries.io \
    --cc=mpm@selenic.com \
    --cc=op-tee@lists.trustedfirmware.org \
    --cc=ricardo@foundries.io \
    --cc=sumit.garg@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Crypto Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-crypto/0 linux-crypto/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-crypto linux-crypto/ https://lore.kernel.org/linux-crypto \
		linux-crypto@vger.kernel.org
	public-inbox-index linux-crypto

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-crypto


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git