On Fri, Feb 23, 2024 at 05:09:18PM +0000, Jonathan Cameron wrote: > On Thu, 22 Feb 2024 14:23:39 -0800 > Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > Clang tripped over a FORTIFY warning in this code, and while it seems it > > may be a false positive in Clang due to loop unwinding, the code in > > question seems to make a lot of assumptions. > > Hi Kees, > > The assumptions are mostly characteristics of how the IIO buffers work > with the scan masks defined based on indexes in the driver provided > struct iio_chan_spec arrays. > > This driver is doing more work than it should need to as we long ago > moved some of the more fiddly handling into the IIO core. > > > Comments added, and the > > Clang warning[1] has been worked around by growing the array size. > > Also there was an uninitialized 4th byte in the __be32 array that was > > being sent through to iio_push_to_buffers(). > > That is indeed not good - the buffer should have been zero initialized. Okay, I'll get this respun and include the fix. > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/2000 [1] > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > Cc: Jonathan Cameron <jic23@xxxxxxxxxx> > > Cc: Lars-Peter Clausen <lars@xxxxxxxxxx> > > Cc: "Uwe Kleine-König" <u.kleine-koenig@xxxxxxxxxxxxxx> > > Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > > Cc: "Nuno Sá" <nuno.sa@xxxxxxxxxx> > > Cc: linux-iio@xxxxxxxxxxxxxxx > > --- > > drivers/iio/pressure/dlhl60d.c | 11 +++++++++-- > > 1 file changed, 9 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/iio/pressure/dlhl60d.c b/drivers/iio/pressure/dlhl60d.c > > index 28c8269ba65d..9bbecd0bfe88 100644 > > --- a/drivers/iio/pressure/dlhl60d.c > > +++ b/drivers/iio/pressure/dlhl60d.c > > @@ -250,20 +250,27 @@ static irqreturn_t dlh_trigger_handler(int irq, void *private) > > struct dlh_state *st = iio_priv(indio_dev); > > int ret; > > unsigned int chn, i = 0; > > - __be32 tmp_buf[2]; > > + /* This was only an array pair of 4 bytes. */ > > True, which is the right size as far as I can tell. > If we need this to suppress a warning then comment should say that. Okay. I think I'll leave it as 2 and manually "unroll" the loop. > > > + __be32 tmp_buf[4] = { }; > > > > ret = dlh_start_capture_and_read(st); > > if (ret) > > goto out; > > > > + /* Nothing was checking masklength vs ARRAY_SIZE(tmp_buf)? */ > > Not needed but no way a compiler could know that. > > > + if (WARN_ON_ONCE(indio_dev->masklength > ARRAY_SIZE(tmp_buf))) > > + goto out; > > + > > for_each_set_bit(chn, indio_dev->active_scan_mask, > > This is all a bit pointless if not 'wrong' other than the > 4th byte uninitialized part. The limit can be hard coded as 2 as > that's a characteristic of this driver. > > For device that always read a particular set of channels they > should provide indio_dev->available_scan_masks = { BIT(1) | BIT(0), 0 }; > and then always push all the data making this always > > memcpy(&tmp_buf[0], &st->rx_buf[1], 3); > mempcy(&tmp_buf[1], &st->rx_buf[1] + 3, 3); Okay, so this could be unrolled manually to check just for bits 0 and 1? > > The buffer demux code in the IIO core will deal with repacking the data > if only one channel is enabled. > > > indio_dev->masklength) { > > - memcpy(tmp_buf + i, > > + /* This is copying 3 bytes. What about the 4th? */ > > + memcpy(&tmp_buf[i], > > &st->rx_buf[1] + chn * DLH_NUM_DATA_BYTES, > > DLH_NUM_DATA_BYTES); > > i++; > > } > > > > + /* How do we know the iio buffer_list has only 2 items? */ > > Can only include items from the channels array at indexes up to the max > scan_index in there, so 0 and 1 in this case (1 might not be present if only > one channel is enabled). Sizes (and alignment) are given by storagebits so > 4 bytes for each. This code pattern seems repeated through all of iio, so I guess we'll leave it as-is. It seems like it'd be nice to have a "length" argument to iio_push_to_buffers(), just to sanity check, but that would need to be a pretty large patch. :P > > > iio_push_to_buffers(indio_dev, tmp_buf); > > > > out: Thanks for looking at this! -Kees -- Kees Cook
