[PATCH v1 0/3] ASoC: Add bounds checking for written values

[Jaroslav Kysela]

On 24. 01. 22 18:08, Takashi Iwai wrote:
> On Mon, 24 Jan 2022 17:52:46 +0100,
> Mark Brown wrote:
>>
>> On Mon, Jan 24, 2022 at 05:29:50PM +0100, Jaroslav Kysela wrote:
>>> On 24. 01. 22 16:32, Mark Brown wrote:
>>
>>>> This series adds verification that values written to registers are in
>>>> bounds for controls since the core doesn't validate for us.
>>
>>> As discussed, those conditions should be optional to eventually catch the
>>> wrong applications. I don't see any benefit to report the range error back
>>> when there is value masking code already. The users will note when the
>>> unwanted values are written to the hardware, or not?
>>
>> In general I'd say that silent failures are harder to work with than
>> returning an error at the point where we notice that there's a problem,
>> assuming userspace is paying any attention to the error return at all of
>> course.  We certainly have quite a lot of existing put() methods that do
>> return errors and it's not like the application isn't invoking undefined
>> behaviour so I don't see a problem here.
> 
> I find also it's more useful to have the proper checks in general.
> 
> Jaroslav, is you concern only about the compatibility of user-space?
> Or anything else?  The compatibility is always certainly a slight
> issue; if this breaks really something useful and actually working
> stuff, we need to consider the workaround...

My concern is only based on the fact that this code is normally not reachable. 
It only costs some CPU ticks and adds extra code to the drivers without any 
other benefit. The applications should not use out of range values and if they 
do, the behavior is not defined (the drivers should only avoid crashes).

The code seems to be added only to make things consistent for the test 
applications. I don't think that it's worth to care only for this reason. What 
is the goal for this code? The result with the proposed code will be - the SoC 
core has the extra validation conditions.

The user space can eventually add similar checks to detect the broken 
applications.

Basically, I think that those checks should be marked as debug and they should 
be optional like we do for CONFIG_SND_CTL_VALIDATION and enable only the fast 
path by default.

					Jaroslav

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.