Re: [PATCH v2 0/2] Sanity-check available_scan_masks array

[Matti Vaittinen]

On 10/28/23 19:32, Jonathan Cameron wrote:
> On Sat, 21 Oct 2023 19:03:15 +0300
> Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
>
> > On 10/21/23 18:55, Jonathan Cameron wrote:
> > > On Mon, 16 Oct 2023 14:04:11 +0300
> > > Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> > >    
> > > > Sanity-check available_scan_masks array
> > > >
> > > > The available_scan_masks is an array of bitmasks representing the
> > > > channels which can be simultaneously(*) scanned by a driver from the
> > > > device. Following special characteristics apply:
> > > >
> > > > - When IIO is scanning through the array it will use the first mask
> > > >     which can be used to scan all enabled channels. This means drivers
> > > >     should order the array in the order of the preference. This does also
> > > >     mean that a mask which is a subset of a mask located earler in array
> > > >     will never be used because the earlier one will be picked by the core.
> > > > - Masks wider than size of long are supported only to some extent. The
> > > >     code scanning through the array will interpret the first mask with
> > > >     first long zeroed as end-of-array terminator. Changing this behaviour
> > > >     would make mask-arrays for multi-long masks to be terminated by more
> > > >     than one zero long. Failure to do so would result kernel to read
> > > >     beyond the array generating a potentially hazardous bug.
> > > >
> > > > Add a sanity-check to IIO-device registration emitting a warning if
> > > > available_scan_mask array is misordered or if mask width is larger than
> > > > a long while available_scan_mask-array is populated. Currently there
> > > > should be no in-tree drivers with available_scan_mask populated and mask
> > > > wider than a long.
> > > >
> > > > Revision history:
> > > > v1 => v2:
> > > > 	- Add patch 2/2 documenting why iio_scan_mask_match() checks only
> > > > 	  a long worth of bits while searching for the end of the
> > > > 	  available_scan_mask-array.
> > > > 	- Styling of patch 1/2 as per comments from Jonathan
> > > > 	v1 and related discussion here:
> > > > 	https://lore.kernel.org/lkml/ZRvjuZaQWdZw1U1I@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> > > >
> > > > Matti Vaittinen (2):
> > > >     iio: sanity check available_scan_masks array
> > > >     iio: buffer: document known issue

...

> I've started queuing stuff up for rebasing post merge window, so I've
> added this as well. For now will only be exposed as the testing branch
> that 0-day pokes at.

Thanks Jonathan!


--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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