linux-kernel - Re: [PATCH v2 0/2] Sanity-check available_scan

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Message-ID: <5d63087a-91c8-434e-aa47-a3d60e456e1f@gmail.com>
Date:   Sun, 29 Oct 2023 17:28:54 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Sanity-check available_scan_masks array

On 10/28/23 19:32, Jonathan Cameron wrote:
> On Sat, 21 Oct 2023 19:03:15 +0300
> Matti Vaittinen <mazziesaccount@...il.com> wrote:
> 
>> On 10/21/23 18:55, Jonathan Cameron wrote:
>>> On Mon, 16 Oct 2023 14:04:11 +0300
>>> Matti Vaittinen <mazziesaccount@...il.com> 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@dc78bmyyyyyyyyyyyyydt-3.rev.dnainternet.fi/
>>>>
>>>> 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

~~ When things go utterly wrong vim users can always type :help! ~~