[PATCH] firmware: arm_scmi: avoid returning uninialized data

[PATCH] firmware: arm_scmi: avoid returning uninialized data

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

Clang notices that there is a code path through
scmi_powercap_notify_supported() that returns an
undefined value:

drivers/firmware/arm_scmi/powercap.c:821:11: error: variable 'supported' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
  821 |         else if (evt_id == SCMI_EVENT_POWERCAP_MEASUREMENTS_CHANGED)
      |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/firmware/arm_scmi/powercap.c:824:9: note: uninitialized use occurs here
  824 |         return supported;
      |                ^~~~~~~~~
drivers/firmware/arm_scmi/powercap.c:821:7: note: remove the 'if' if its condition is always true
  821 |         else if (evt_id == SCMI_EVENT_POWERCAP_MEASUREMENTS_CHANGED)
      |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  822 |                 supported = dom_info->notify_powercap_measurement_change;
drivers/firmware/arm_scmi/powercap.c:811:16: note: initialize the variable 'supported' to silence this warning
  811 |         bool supported;
      |                       ^

Return 'false' here, which is probably what was intended.

Fixes: c92a75fe84ce ("firmware: arm_scmi: Implement Powercap .is_notify_supported callback")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/firmware/arm_scmi/powercap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/firmware/arm_scmi/powercap.c b/drivers/firmware/arm_scmi/powercap.c
index aae91f47303e..8ee3be8776b0 100644
--- a/drivers/firmware/arm_scmi/powercap.c
+++ b/drivers/firmware/arm_scmi/powercap.c
@@ -820,6 +820,8 @@ scmi_powercap_notify_supported(const struct scmi_protocol_handle *ph,
 		supported = dom_info->notify_powercap_cap_change;
 	else if (evt_id == SCMI_EVENT_POWERCAP_MEASUREMENTS_CHANGED)
 		supported = dom_info->notify_powercap_measurement_change;
+	else
+		supported = false;
 
 	return supported;
 }
-- 
2.39.2


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Re: [PATCH] firmware: arm_scmi: avoid returning uninialized data

[Cristian Marussi]

On Fri, Feb 16, 2024 at 05:32:53PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Clang notices that there is a code path through
> scmi_powercap_notify_supported() that returns an
> undefined value:
> 

Hi Arnd,

> drivers/firmware/arm_scmi/powercap.c:821:11: error: variable 'supported' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>   821 |         else if (evt_id == SCMI_EVENT_POWERCAP_MEASUREMENTS_CHANGED)
>       |                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/firmware/arm_scmi/powercap.c:824:9: note: uninitialized use occurs here
>   824 |         return supported;
>       |                ^~~~~~~~~
> drivers/firmware/arm_scmi/powercap.c:821:7: note: remove the 'if' if its condition is always true
>   821 |         else if (evt_id == SCMI_EVENT_POWERCAP_MEASUREMENTS_CHANGED)
>       |              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   822 |                 supported = dom_info->notify_powercap_measurement_change;
> drivers/firmware/arm_scmi/powercap.c:811:16: note: initialize the variable 'supported' to silence this warning
>   811 |         bool supported;
>       |                       ^
> 
> Return 'false' here, which is probably what was intended.
> 
> Fixes: c92a75fe84ce ("firmware: arm_scmi: Implement Powercap .is_notify_supported callback")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

thanks for looking at this, this series that I've just posted is still
to be reviewd at all, so I would expect issues :D...BUT in this case I
dont think that the clang report is valid since, inside the culprit
function scmi_powercap_notify_supported(), a few lines before the
reported usage of unitialized data there is a check (@line 816) on the
'bounds' of evt_id itself

	if (evt_id >= ARRAY_SIZE(evt_2_cmd) || src_id >= pi->num_domains)
		return false;

so basically the mentioned if/else WILL be evaluated in some of its
branches for sure and supported wont be uninitialized.

Indeed, I removed from here (and from all the series) the explicit
initialization at definition time right before posting the series.

Having saidm that...maybe it is just brain-dead this approach of mine
since it is able to fool clang & friends...I would add bACK an explicit
initialization of supported all across this series in V2, if this
sounds good to you.

Thanks,
Cristian


> ---
>  drivers/firmware/arm_scmi/powercap.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/firmware/arm_scmi/powercap.c b/drivers/firmware/arm_scmi/powercap.c
> index aae91f47303e..8ee3be8776b0 100644
> --- a/drivers/firmware/arm_scmi/powercap.c
> +++ b/drivers/firmware/arm_scmi/powercap.c
> @@ -820,6 +820,8 @@ scmi_powercap_notify_supported(const struct scmi_protocol_handle *ph,
>  		supported = dom_info->notify_powercap_cap_change;
>  	else if (evt_id == SCMI_EVENT_POWERCAP_MEASUREMENTS_CHANGED)
>  		supported = dom_info->notify_powercap_measurement_change;
> +	else
> +		supported = false;
>  
>  	return supported;
>  }
> -- 
> 2.39.2
> 

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Re: [PATCH] firmware: arm_scmi: avoid returning uninialized data

[Arnd Bergmann]

On Fri, Feb 16, 2024, at 18:21, Cristian Marussi wrote:
> On Fri, Feb 16, 2024 at 05:32:53PM +0100, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>> 
>> Clang notices that there is a code path through
>> scmi_powercap_notify_supported() that returns an
>> undefined value:
>> 
>
> thanks for looking at this, this series that I've just posted is still
> to be reviewd at all, so I would expect issues :D...BUT in this case I
> dont think that the clang report is valid since, inside the culprit
> function scmi_powercap_notify_supported(), a few lines before the
> reported usage of unitialized data there is a check (@line 816) on the
> 'bounds' of evt_id itself
>
> 	if (evt_id >= ARRAY_SIZE(evt_2_cmd) || src_id >= pi->num_domains)
> 		return false;
>
> so basically the mentioned if/else WILL be evaluated in some of its
> branches for sure and supported wont be uninitialized.
>
> Indeed, I removed from here (and from all the series) the explicit
> initialization at definition time right before posting the series.
>
> Having saidm that...maybe it is just brain-dead this approach of mine
> since it is able to fool clang & friends...I would add bACK an explicit
> initialization of supported all across this series in V2, if this
> sounds good to you.

I'm fine with any solution that avoids the warning. I usually
prefer the explicit assignment where it's needed over having
it as part of the declaration, and in this case I would
probably pick a switch/case of a set of if/else fi/else
blocks

     Arnd

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