Re: [PATCH 19/32] iio:imu:st_lsm6dsx Fix alignment and data leak issues

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> 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 set of suitable structures in the iio_priv() data.
> 
> This data is allocated with kzalloc so no data can leak apart from
> previous readings.
> 
> For the tagged path the data is aligned by using __aligned(8) for
> the buffer on the stack.
> 
> There has been a lot of churn in this driver, so likely backports
> may be needed for stable.

Hi Jonathan,

I added just some nitpicks inline, but it seems to me the patch is fine.
I guess we can address them with a followup patch if you agree, no need to
resend this huge series :)

Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>

> 
> Fixes: 290a6ce11d93 ("iio: imu: add support to lsm6dsx driver")
> Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> Cc: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
>  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       |  5 +++
>  .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    | 36 ++++++++++---------
>  2 files changed, 25 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> index b56df409ed0f..5f821ef467da 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> @@ -411,6 +411,11 @@ struct st_lsm6dsx_hw {
>  	const struct st_lsm6dsx_settings *settings;
>  
>  	struct iio_mount_matrix orientation;
> +	/* Ensure natural alignment of buffer elements */
> +	struct {
> +		__le16 channels[3];
> +		s64 ts __aligned(8);
> +	} gyro_scan, acc_scan, ext_scan;
>  };

it seems to me doing something like:

struct {
	__le16 channels[3];
	s64 ts __aligned(8);
} scan[3];

would be better if for example we want to add support for more external devices
for untagged FIFO devices

>  
>  static __maybe_unused const struct iio_event_spec st_lsm6dsx_event = {
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> index afd00daeefb2..bebbc2bb37f7 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> @@ -341,9 +341,6 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
>  	int err, sip, acc_sip, gyro_sip, ts_sip, ext_sip, read_len, offset;
>  	u16 fifo_len, pattern_len = hw->sip * ST_LSM6DSX_SAMPLE_SIZE;
>  	u16 fifo_diff_mask = hw->settings->fifo_ops.fifo_diff.mask;
> -	u8 gyro_buff[ST_LSM6DSX_IIO_BUFF_SIZE];
> -	u8 acc_buff[ST_LSM6DSX_IIO_BUFF_SIZE];
> -	u8 ext_buff[ST_LSM6DSX_IIO_BUFF_SIZE];
>  	bool reset_ts = false;
>  	__le16 fifo_status;
>  	s64 ts = 0;
> @@ -404,19 +401,22 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
>  
>  		while (acc_sip > 0 || gyro_sip > 0 || ext_sip > 0) {
>  			if (gyro_sip > 0 && !(sip % gyro_sensor->decimator)) {
> -				memcpy(gyro_buff, &hw->buff[offset],
> -				       ST_LSM6DSX_SAMPLE_SIZE);
> -				offset += ST_LSM6DSX_SAMPLE_SIZE;
> +				memcpy(hw->gyro_scan.channels,
> +				       &hw->buff[offset],
> +				       sizeof(hw->gyro_scan.channels));
> +				offset += sizeof(hw->gyro_scan.channels);
>  			}
>  			if (acc_sip > 0 && !(sip % acc_sensor->decimator)) {
> -				memcpy(acc_buff, &hw->buff[offset],
> -				       ST_LSM6DSX_SAMPLE_SIZE);
> -				offset += ST_LSM6DSX_SAMPLE_SIZE;
> +				memcpy(hw->acc_scan.channels,
> +				       &hw->buff[offset],
> +				       sizeof(hw->acc_scan.channels));
> +				offset += sizeof(hw->acc_scan.channels);
>  			}
>  			if (ext_sip > 0 && !(sip % ext_sensor->decimator)) {
> -				memcpy(ext_buff, &hw->buff[offset],
> -				       ST_LSM6DSX_SAMPLE_SIZE);
> -				offset += ST_LSM6DSX_SAMPLE_SIZE;
> +				memcpy(hw->ext_scan.channels,
> +				       &hw->buff[offset],
> +				       sizeof(hw->ext_scan.channels));
> +				offset += sizeof(hw->ext_scan.channels);
>  			}
>  
>  			if (ts_sip-- > 0) {
> @@ -446,19 +446,22 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
>  			if (gyro_sip > 0 && !(sip % gyro_sensor->decimator)) {
>  				iio_push_to_buffers_with_timestamp(
>  					hw->iio_devs[ST_LSM6DSX_ID_GYRO],
> -					gyro_buff, gyro_sensor->ts_ref + ts);
> +					&hw->gyro_scan,
> +					gyro_sensor->ts_ref + ts);
>  				gyro_sip--;
>  			}
>  			if (acc_sip > 0 && !(sip % acc_sensor->decimator)) {
>  				iio_push_to_buffers_with_timestamp(
>  					hw->iio_devs[ST_LSM6DSX_ID_ACC],
> -					acc_buff, acc_sensor->ts_ref + ts);
> +					&hw->acc_scan,
> +					acc_sensor->ts_ref + ts);
>  				acc_sip--;
>  			}
>  			if (ext_sip > 0 && !(sip % ext_sensor->decimator)) {
>  				iio_push_to_buffers_with_timestamp(
>  					hw->iio_devs[ST_LSM6DSX_ID_EXT0],
> -					ext_buff, ext_sensor->ts_ref + ts);
> +					&hw->ext_scan,
> +					ext_sensor->ts_ref + ts);
>  				ext_sip--;
>  			}
>  			sip++;
> @@ -543,7 +546,8 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
>  {
>  	u16 pattern_len = hw->sip * ST_LSM6DSX_TAGGED_SAMPLE_SIZE;
>  	u16 fifo_len, fifo_diff_mask;
> -	u8 iio_buff[ST_LSM6DSX_IIO_BUFF_SIZE], tag;
> +	u8 iio_buff[ST_LSM6DSX_IIO_BUFF_SIZE] __aligned(8);

here we can use hw->scan[0] and drop the array on the stack

> +	u8 tag;
>  	bool reset_ts = false;
>  	int i, err, read_len;
>  	__le16 fifo_status;
> -- 
> 2.26.2
> 

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