| Message ID | 20200607155408.958437-28-jic23@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | IIO: Fused set 1 and 2 of timestamp alignment fixes | expand |
On Sun, Jun 07, 2020 at 04:54:03PM +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. > As Lars also noted this anti pattern can involve a leak of data to > userspace and that indeed can happen here. We close both issues by > moving to a suitable structure in the iio_priv() data with alignment > explicitly requested. This data is allocated with kzalloc so no > data can leak apart from previous readings. > + /* > + * Used to correctly align data. > + * Ensure timestamp is naturally aligned. > + */ > + u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8); Can't you rather provide a struct as well?
On Mon, 8 Jun 2020 16:14:58 +0300 Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > On Sun, Jun 07, 2020 at 04:54:03PM +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. > > As Lars also noted this anti pattern can involve a leak of data to > > userspace and that indeed can happen here. We close both issues by > > moving to a suitable structure in the iio_priv() data with alignment > > explicitly requested. This data is allocated with kzalloc so no > > data can leak apart from previous readings. > > > + /* > > + * Used to correctly align data. > > + * Ensure timestamp is naturally aligned. > > + */ > > > + u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8); > > Can't you rather provide a struct as well? > Not without giving a false impression of where the time stamp is in the resulting buffer. I'm not keen to do that because it'll lead to people fundamentally misunderstanding the dynamic nature of IIO buffer packing. Here it could start at byte 8, 16, 24, 32, 48, 64 I think. It's more than possible I've gotten one of these wrong and missed a restriction on the layout in a given device though! Jonathan
On Mon, Jun 08, 2020 at 03:06:40PM +0100, Jonathan Cameron wrote: > On Mon, 8 Jun 2020 16:14:58 +0300 > Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote: > > > On Sun, Jun 07, 2020 at 04:54:03PM +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. > > > As Lars also noted this anti pattern can involve a leak of data to > > > userspace and that indeed can happen here. We close both issues by > > > moving to a suitable structure in the iio_priv() data with alignment > > > explicitly requested. This data is allocated with kzalloc so no > > > data can leak apart from previous readings. > > > > > + /* > > > + * Used to correctly align data. > > > + * Ensure timestamp is naturally aligned. > > > + */ > > > > > + u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8); > > > > Can't you rather provide a struct as well? > > > Not without giving a false impression of where the time stamp is in the resulting > buffer. > > I'm not keen to do that because it'll lead to people fundamentally misunderstanding > the dynamic nature of IIO buffer packing. > > Here it could start at byte 8, 16, 24, 32, 48, 64 I think. I see, thanks for explanation! Same for the other comment.
diff --git a/drivers/iio/adc/ti-ads124s08.c b/drivers/iio/adc/ti-ads124s08.c index dacaa7255a3b..f9731e6a4260 100644 --- a/drivers/iio/adc/ti-ads124s08.c +++ b/drivers/iio/adc/ti-ads124s08.c @@ -99,6 +99,11 @@ struct ads124s_private { struct gpio_desc *reset_gpio; struct spi_device *spi; struct mutex lock; + /* + * Used to correctly align data. + * Ensure timestamp is naturally aligned. + */ + u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)] __aligned(8); u8 data[5] ____cacheline_aligned; }; @@ -269,7 +274,6 @@ static irqreturn_t ads124s_trigger_handler(int irq, void *p) struct iio_poll_func *pf = p; struct iio_dev *indio_dev = pf->indio_dev; struct ads124s_private *priv = iio_priv(indio_dev); - u32 buffer[ADS124S08_MAX_CHANNELS + sizeof(s64)/sizeof(u16)]; int scan_index, j = 0; int ret; @@ -284,7 +288,7 @@ static irqreturn_t ads124s_trigger_handler(int irq, void *p) if (ret) dev_err(&priv->spi->dev, "Start ADC conversions failed\n"); - buffer[j] = ads124s_read(indio_dev, scan_index); + priv->buffer[j] = ads124s_read(indio_dev, scan_index); ret = ads124s_write_cmd(indio_dev, ADS124S08_STOP_CONV); if (ret) dev_err(&priv->spi->dev, "Stop ADC conversions failed\n"); @@ -292,7 +296,7 @@ static irqreturn_t ads124s_trigger_handler(int irq, void *p) j++; } - iio_push_to_buffers_with_timestamp(indio_dev, buffer, + iio_push_to_buffers_with_timestamp(indio_dev, priv->buffer, pf->timestamp); iio_trigger_notify_done(indio_dev->trig);