[PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Antonio Quartulli]

acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
would result in dereferencing buffer.pointer (obj) while being NULL.

Bail out also when status is AE_NOT_FOUND with a proper error message.

This fixes 1 FORWARD_NULL issue reported by Coverity
Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)

Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
index cce85389427f..f10c3261a4ab 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
@@ -172,10 +172,13 @@ static union acpi_object *amdgpu_atif_call(struct amdgpu_atif *atif,
 				      &buffer);
 	obj = (union acpi_object *)buffer.pointer;
 
-	/* Fail if calling the method fails and ATIF is supported */
-	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
-		DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
-				 acpi_format_exception(status));
+	/* Fail if calling the method fails */
+	if (ACPI_FAILURE(status)) {
+		if (status != AE_NOT_FOUND)
+			DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
+					 acpi_format_exception(status));
+		else
+			DRM_DEBUG_DRIVER("ATIF not supported\n");
 		kfree(obj);
 		return NULL;
 	}
-- 
2.45.2

Re: [PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Mario Limonciello]

On 10/29/2024 18:32, Antonio Quartulli wrote:
> acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
> would result in dereferencing buffer.pointer (obj) while being NULL.
> 
> Bail out also when status is AE_NOT_FOUND with a proper error message.
> 
> This fixes 1 FORWARD_NULL issue reported by Coverity
> Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)
> 
> Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>

I'm not really sure how realistic this failure is.  Can you share the 
full call trace that Coverity identified?

amdgpu_atif_pci_probe_handle() will check whether the handle is 
available in the first place.  We'll never this this far if that failed.

Because of that I don't follow how this could return AE_NOT_FOUND.
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> index cce85389427f..f10c3261a4ab 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> @@ -172,10 +172,13 @@ static union acpi_object *amdgpu_atif_call(struct amdgpu_atif *atif,
>   				      &buffer);
>   	obj = (union acpi_object *)buffer.pointer;
>   
> -	/* Fail if calling the method fails and ATIF is supported */
> -	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> -		DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
> -				 acpi_format_exception(status));
> +	/* Fail if calling the method fails */
> +	if (ACPI_FAILURE(status)) {
> +		if (status != AE_NOT_FOUND)
> +			DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
> +					 acpi_format_exception(status));
> +		else
> +			DRM_DEBUG_DRIVER("ATIF not supported\n");
>   		kfree(obj);
>   		return NULL;
>   	}

Re: [PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Antonio Quartulli]

Hi Mario,

On 30/10/2024 02:41, Mario Limonciello wrote:
> On 10/29/2024 18:32, Antonio Quartulli wrote:
>> acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
>> would result in dereferencing buffer.pointer (obj) while being NULL.
>>
>> Bail out also when status is AE_NOT_FOUND with a proper error message.
>>
>> This fixes 1 FORWARD_NULL issue reported by Coverity
>> Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)
>>
>> Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
> 
> I'm not really sure how realistic this failure is.  Can you share the 
> full call trace that Coverity identified?

I just checked Coverity Scan and it only says:

	5. Condition status, taking true branch.
	6. Condition status != 5U /* (acpi_status)(5 | 0) */, taking false branch.

The above points are related to:

	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)

It doesn't show how acpi_evaluate_object() is expected to return 
AE_NOT_FOUND.

This said, if you think this case is unrealistic, why do you check for 
"status != AE_NOT_FOUND" at all?

At this point maybe it would make more sense to simply drop this check 
and always bail out with the current error message.

Basically a patch with the following only:

-       /* Fail if calling the method fails and ATIF is supported */
-       if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
+       /* Fail if calling the method fails */
+       if (ACPI_FAILURE(status)) {

This way we don't make a fuzz for a possibly unrealistic case, while 
still protecting against bugs and null-dereferences.


Regards,

> 
> amdgpu_atif_pci_probe_handle() will check whether the handle is 
> available in the first place.  We'll never this this far if that failed.
> 
> Because of that I don't follow how this could return AE_NOT_FOUND.
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
>>   1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/ 
>> drm/amd/amdgpu/amdgpu_acpi.c
>> index cce85389427f..f10c3261a4ab 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>> @@ -172,10 +172,13 @@ static union acpi_object 
>> *amdgpu_atif_call(struct amdgpu_atif *atif,
>>                         &buffer);
>>       obj = (union acpi_object *)buffer.pointer;
>> -    /* Fail if calling the method fails and ATIF is supported */
>> -    if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
>> -        DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>> -                 acpi_format_exception(status));
>> +    /* Fail if calling the method fails */
>> +    if (ACPI_FAILURE(status)) {
>> +        if (status != AE_NOT_FOUND)
>> +            DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>> +                     acpi_format_exception(status));
>> +        else
>> +            DRM_DEBUG_DRIVER("ATIF not supported\n");
>>           kfree(obj);
>>           return NULL;
>>       }
> 

-- 
Antonio Quartulli

CEO and Co-Founder
Mandelbit Srl
https://www.mandelbit.com

Re: [PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Mario Limonciello]

On 10/30/2024 16:06, Antonio Quartulli wrote:
> Hi Mario,
> 
> On 30/10/2024 02:41, Mario Limonciello wrote:
>> On 10/29/2024 18:32, Antonio Quartulli wrote:
>>> acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
>>> would result in dereferencing buffer.pointer (obj) while being NULL.
>>>
>>> Bail out also when status is AE_NOT_FOUND with a proper error message.
>>>
>>> This fixes 1 FORWARD_NULL issue reported by Coverity
>>> Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)
>>>
>>> Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
>>
>> I'm not really sure how realistic this failure is.  Can you share the 
>> full call trace that Coverity identified?
> 
> I just checked Coverity Scan and it only says:
> 
>      5. Condition status, taking true branch.
>      6. Condition status != 5U /* (acpi_status)(5 | 0) */, taking false 
> branch.
> 
> The above points are related to:
> 
>      if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)
> 
> It doesn't show how acpi_evaluate_object() is expected to return 
> AE_NOT_FOUND.
> 
> This said, if you think this case is unrealistic, why do you check for 
> "status != AE_NOT_FOUND" at all?
> 
> At this point maybe it would make more sense to simply drop this check 
> and always bail out with the current error message.
> 
> Basically a patch with the following only:
> 
> -       /* Fail if calling the method fails and ATIF is supported */
> -       if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> +       /* Fail if calling the method fails */
> +       if (ACPI_FAILURE(status)) {
> 
> This way we don't make a fuzz for a possibly unrealistic case, while 
> still protecting against bugs and null-dereferences.

Yeah I think that's a good idea.  Can you respin it as a v2?

> 
> 
> Regards,
> 
>>
>> amdgpu_atif_pci_probe_handle() will check whether the handle is 
>> available in the first place.  We'll never this this far if that failed.
>>
>> Because of that I don't follow how this could return AE_NOT_FOUND.
>>> ---
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
>>>   1 file changed, 7 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/ 
>>> drm/amd/amdgpu/amdgpu_acpi.c
>>> index cce85389427f..f10c3261a4ab 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>>> @@ -172,10 +172,13 @@ static union acpi_object 
>>> *amdgpu_atif_call(struct amdgpu_atif *atif,
>>>                         &buffer);
>>>       obj = (union acpi_object *)buffer.pointer;
>>> -    /* Fail if calling the method fails and ATIF is supported */
>>> -    if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
>>> -        DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>>> -                 acpi_format_exception(status));
>>> +    /* Fail if calling the method fails */
>>> +    if (ACPI_FAILURE(status)) {
>>> +        if (status != AE_NOT_FOUND)
>>> +            DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>>> +                     acpi_format_exception(status));
>>> +        else
>>> +            DRM_DEBUG_DRIVER("ATIF not supported\n");
>>>           kfree(obj);
>>>           return NULL;
>>>       }
>>
> 

Re: [PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not supported

[Antonio Quartulli]

On 31/10/2024 15:41, Mario Limonciello wrote:
> On 10/30/2024 16:06, Antonio Quartulli wrote:
>> Hi Mario,
>>
>> On 30/10/2024 02:41, Mario Limonciello wrote:
>>> On 10/29/2024 18:32, Antonio Quartulli wrote:
>>>> acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
>>>> would result in dereferencing buffer.pointer (obj) while being NULL.
>>>>
>>>> Bail out also when status is AE_NOT_FOUND with a proper error message.
>>>>
>>>> This fixes 1 FORWARD_NULL issue reported by Coverity
>>>> Report: CID 1600951:  Null pointer dereferences  (FORWARD_NULL)
>>>>
>>>> Signed-off-by: Antonio Quartulli <antonio@mandelbit.com>
>>>
>>> I'm not really sure how realistic this failure is.  Can you share the 
>>> full call trace that Coverity identified?
>>
>> I just checked Coverity Scan and it only says:
>>
>>      5. Condition status, taking true branch.
>>      6. Condition status != 5U /* (acpi_status)(5 | 0) */, taking 
>> false branch.
>>
>> The above points are related to:
>>
>>      if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)
>>
>> It doesn't show how acpi_evaluate_object() is expected to return 
>> AE_NOT_FOUND.
>>
>> This said, if you think this case is unrealistic, why do you check for 
>> "status != AE_NOT_FOUND" at all?
>>
>> At this point maybe it would make more sense to simply drop this check 
>> and always bail out with the current error message.
>>
>> Basically a patch with the following only:
>>
>> -       /* Fail if calling the method fails and ATIF is supported */
>> -       if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
>> +       /* Fail if calling the method fails */
>> +       if (ACPI_FAILURE(status)) {
>>
>> This way we don't make a fuzz for a possibly unrealistic case, while 
>> still protecting against bugs and null-dereferences.
> 
> Yeah I think that's a good idea.  Can you respin it as a v2?

Will do!
Thanks for your feedback, Mario.

Regards,

> 
>>
>>
>> Regards,
>>
>>>
>>> amdgpu_atif_pci_probe_handle() will check whether the handle is 
>>> available in the first place.  We'll never this this far if that failed.
>>>
>>> Because of that I don't follow how this could return AE_NOT_FOUND.
>>>> ---
>>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
>>>>   1 file changed, 7 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/ 
>>>> drm/amd/amdgpu/amdgpu_acpi.c
>>>> index cce85389427f..f10c3261a4ab 100644
>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>>>> @@ -172,10 +172,13 @@ static union acpi_object 
>>>> *amdgpu_atif_call(struct amdgpu_atif *atif,
>>>>                         &buffer);
>>>>       obj = (union acpi_object *)buffer.pointer;
>>>> -    /* Fail if calling the method fails and ATIF is supported */
>>>> -    if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
>>>> -        DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>>>> -                 acpi_format_exception(status));
>>>> +    /* Fail if calling the method fails */
>>>> +    if (ACPI_FAILURE(status)) {
>>>> +        if (status != AE_NOT_FOUND)
>>>> +            DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>>>> +                     acpi_format_exception(status));
>>>> +        else
>>>> +            DRM_DEBUG_DRIVER("ATIF not supported\n");
>>>>           kfree(obj);
>>>>           return NULL;
>>>>       }
>>>
>>
> 

-- 
Antonio Quartulli

CEO and Co-Founder
Mandelbit Srl
https://www.mandelbit.com