Re: [PATCH 21/32] iio:pressure:ms5611 Fix buffer element alignment

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 7 Jun 2020 20:03:13 +0200
Tomasz Duszynski <tomasz.duszynski@octakon.com> wrote:

> On Sun, Jun 07, 2020 at 04:53:57PM +0100, Jonathan Cameron wrote:
> > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >
> > One of a class of bugs pointed out by Lars in a recent review.
> > iio_push_to_buffers_with_timestamp assumes the buffer used is aligned
> > to the size of the timestamp (8 bytes).  This is not guaranteed in
> > this driver which uses an array of smaller elements on the stack.
> > Here there is no data leak possibility so use an explicit structure
> > on the stack to ensure alignment and nice readable fashion.
> >
> > The forced alignment of ts isn't strictly necessary in this driver
> > as the padding will be correct anyway (there isn't any).  However
> > it is probably less fragile to have it there and it acts as
> > documentation of the requirement.
> >  
> 
> Looks good.
> Acked-by: Tomasz Duszynski <tomasz.duszynski@octakon.com>
Applied to the fixes-togreg branch of iio.git and marked for stable.
I'm picking up those patch in the series for which I have an ack to
cut down on the number we need to consider in the next version.

Thanks,

Jonathan

> 
> > Fixes: 713bbb4efb9dc ("iio: pressure: ms5611: Add triggered buffer support")
> > Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >  drivers/iio/pressure/ms5611_core.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iio/pressure/ms5611_core.c b/drivers/iio/pressure/ms5611_core.c
> > index d451bb9dffc8..214b0d25f598 100644
> > --- a/drivers/iio/pressure/ms5611_core.c
> > +++ b/drivers/iio/pressure/ms5611_core.c
> > @@ -212,16 +212,21 @@ static irqreturn_t ms5611_trigger_handler(int irq, void *p)
> >  	struct iio_poll_func *pf = p;
> >  	struct iio_dev *indio_dev = pf->indio_dev;
> >  	struct ms5611_state *st = iio_priv(indio_dev);
> > -	s32 buf[4]; /* s32 (pressure) + s32 (temp) + 2 * s32 (timestamp) */
> > +	/* Ensure buffer elements are naturally aligned */
> > +	struct {
> > +		s32 channels[2];
> > +		s64 ts __aligned(8);
> > +	} scan;
> >  	int ret;
> >
> >  	mutex_lock(&st->lock);
> > -	ret = ms5611_read_temp_and_pressure(indio_dev, &buf[1], &buf[0]);
> > +	ret = ms5611_read_temp_and_pressure(indio_dev, &scan.channels[1],
> > +					    &scan.channels[0]);
> >  	mutex_unlock(&st->lock);
> >  	if (ret < 0)
> >  		goto err;
> >
> > -	iio_push_to_buffers_with_timestamp(indio_dev, buf,
> > +	iio_push_to_buffers_with_timestamp(indio_dev, &scan,
> >  					   iio_get_time_ns(indio_dev));
> >
> >  err:
> > --
> > 2.26.2
> >