Re: [PATCH v3 3/6] crypto: Add Qcom prng driver

Stephan Mueller
2018-07-04T06:16:50Z

Am Mittwoch, 4. Juli 2018, 08:10:35 CEST schrieb Vinod:

Hi Vinod,

> On 04-07-18, 09:40, Vinod wrote:
> > Hi Stephan,
> >
> > On 03-07-18, 15:28, Stephan Mueller wrote:
> > > Am Dienstag, 3. Juli 2018, 08:04:31 CEST schrieb Vinod Koul:
> > > > +static int qcom_rng_read(struct qcom_rng *rng, void *data, size_t
> > > > max)
> > > > +{
> > > > + size_t currsize = 0;
> > > > + u32 *retdata = data;
> > >
> > > How can you be sure that this cast is appropriate? I.e. how is it
> > > guaranteed that data is 4-byte aligned?
> >
> > While reading we check the alignment:
> > /* make sure we stay on 32bit boundary */
> > if ((max - currsize) < WORD_SZ)
> >
> > break;

I am not sure I follow your argument.

You cast a void (or u8 pointer into u32:

+ u32 *retdata = data;

You use it:

+ *retdata++ = val;

Followed by your check.

What I mean is that the initial cast and then the subsequent write operation
is only guaranteed to work if the initial pointer is alighed on a 4 byte
boundary. However, since it is an u8 pointer, it is not guaranteed to be
aligned.

So, I guess you want to use memcpy (at least if it is not aligned).

Ciao
Stephan