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Message-ID: <20240223174551.00007411@Huawei.com>
Date: Fri, 23 Feb 2024 17:45:51 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Kees Cook <keescook@...omium.org>
CC: Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>,
Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, Andy
Shevchenko <andriy.shevchenko@...ux.intel.com>, Nuno Sá
<nuno.sa@...log.com>, <linux-iio@...r.kernel.org>, Nathan Chancellor
<nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, "Bill
Wendling" <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
<linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>,
<linux-hardening@...r.kernel.org>
Subject: Re: [PATCH] [RFC] iio: pressure: dlhl60d: Check mask_width for IRQs
On Fri, 23 Feb 2024 09:14:53 -0800
Kees Cook <keescook@...omium.org> wrote:
> 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@...omium.org> 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@...omium.org>
> > > ---
> > > Cc: Jonathan Cameron <jic23@...nel.org>
> > > Cc: Lars-Peter Clausen <lars@...afoo.de>
> > > Cc: "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de>
> > > Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > Cc: "Nuno Sá" <nuno.sa@...log.com>
> > > Cc: linux-iio@...r.kernel.org
> > > ---
> > > 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.
Without the available mask that is a little fiddly you'll have
deal with channel 0 only enabled, channel 1 only enabled and
both channels 0 and channel 1 enabled.
Not too bad though as only 2 channels.
>
> >
> > > + __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?
Ideally it wouldn't check them - the hardwork has been done to read both
channels anyway and the IIO core handles userspace or in kernel consumers
that want a subset of what is enabled, but that needs the available_scan_masks
to be set so that the IIO core knows all channels always enabled.
>
> >
> > 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
yeah. Hindsight!
We could add it in an incremental fashion though
iio_push_to_bufs(struct iio_dev *indio_dev, void *buf, size_t buf_len)
with a length parameter. The oddity that is
iio_push_to_buffers_with_timestamp() would benefit here as that needs
a bigger buffer than immediately apparent in the driver and we've
had a few bugs around that over the years.
It would probably be a one way check.
I might have a play and see how useful this would be.
>
> >
> > > iio_push_to_buffers(indio_dev, tmp_buf);
> > >
> > > out:
>
> Thanks for looking at this!
>
> -Kees
>
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