Subject: Re: [PATCH] drm/amdkfd: Fix potential NULL pointer dereferences
To: "Gustavo A. R. Silva" <garsilva@embeddedor.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        David Airlie <airlied@linux.ie>, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <20180110165008.GA10691@embeddedor.com>
 <c4197e6a-ba58-23b9-8fa8-8a9b3ff74ef9@amd.com>
 <20180110155849.Horde.DDGbi3ysasL2eHmvZ4k8adb@gator4166.hostgator.com>
From: Felix Kuehling <felix.kuehling@amd.com>
Organization: AMD Inc.
Message-ID: <413c85ee-aca0-fd86-4792-0d620b9251e2@amd.com>
Date: Wed, 10 Jan 2018 17:26:05 -0500
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Yeah, this looks good to me.

Regards,
  Felix


On 2018-01-10 04:58 PM, Gustavo A. R. Silva wrote:
> Hi Felix,
>
> Quoting Felix Kuehling <felix.kuehling@amd.com>:
>
>> Hi Gustavo,
>>
>> Thanks for catching that. When returning a fault, I think you also need
>> to srcu_read_unlock(&kfd_processes_srcu, idx).
>>
>> However, instead of returning an error, I think I'd prefer to skip PDDs
>> that can't be found with continue statements. That way others would
>> still suspend and resume successfully. Maybe just print a WARN_ON for
>> PDDs that aren't found, because that's an unexpected situation,
>> currently. Maybe in the future it could be normal thing if we ever
>> support GPU hotplug.
>>
>
> I got it. In that case, what do you think about the following patch
> instead?
>
> index a22fb071..4ff5f0f 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> @@ -461,7 +461,8 @@ int kfd_bind_processes_to_device(struct kfd_dev *dev)
>         hash_for_each_rcu(kfd_processes_table, temp, p, kfd_processes) {
>                 mutex_lock(&p->mutex);
>                 pdd = kfd_get_process_device_data(dev, p);
> -               if (pdd->bound != PDD_BOUND_SUSPENDED) {
> +
> +               if (WARN_ON(!pdd) || pdd->bound != PDD_BOUND_SUSPENDED) {
>                         mutex_unlock(&p->mutex);
>                         continue;
>                 }
> @@ -501,6 +502,11 @@ void kfd_unbind_processes_from_device(struct
> kfd_dev *dev)
>                 mutex_lock(&p->mutex);
>                 pdd = kfd_get_process_device_data(dev, p);
>
> +               if (WARN_ON(!pdd)) {
> +                       mutex_unlock(&p->mutex);
> +                       continue;
> +               }
> +
>                 if (pdd->bound == PDD_BOUND)
>                         pdd->bound = PDD_BOUND_SUSPENDED;
>                 mutex_unlock(&p->mutex);
>
>
> Thank you for the feedback.
> -- 
> Gustavo
>
>> Regards,
>>   Felix
>>
>>
>> On 2018-01-10 11:50 AM, Gustavo A. R. Silva wrote:
>>> In case kfd_get_process_device_data returns null, there are some
>>> null pointer dereferences in functions kfd_bind_processes_to_device
>>> and kfd_unbind_processes_from_device.
>>>
>>> Fix this by null checking pdd before dereferencing it.
>>>
>>> Addresses-Coverity-ID: 1463794 ("Dereference null return value")
>>> Addresses-Coverity-ID: 1463772 ("Dereference null return value")
>>> Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
>>> ---
>>>  drivers/gpu/drm/amd/amdkfd/kfd_process.c | 12 ++++++++++++
>>>  1 file changed, 12 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> index a22fb071..29d51d5 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> @@ -461,6 +461,13 @@ int kfd_bind_processes_to_device(struct kfd_dev
>>> *dev)
>>>      hash_for_each_rcu(kfd_processes_table, temp, p, kfd_processes) {
>>>          mutex_lock(&p->mutex);
>>>          pdd = kfd_get_process_device_data(dev, p);
>>> +
>>> +        if (!pdd) {
>>> +            pr_err("Process device data doesn't exist\n");
>>> +            mutex_unlock(&p->mutex);
>>> +            return -EFAULT;
>>> +        }
>>> +
>>>          if (pdd->bound != PDD_BOUND_SUSPENDED) {
>>>              mutex_unlock(&p->mutex);
>>>              continue;
>>> @@ -501,6 +508,11 @@ void kfd_unbind_processes_from_device(struct
>>> kfd_dev *dev)
>>>          mutex_lock(&p->mutex);
>>>          pdd = kfd_get_process_device_data(dev, p);
>>>
>>> +        if (!pdd) {
>>> +            mutex_unlock(&p->mutex);
>>> +            return;
>>> +        }
>>> +
>>>          if (pdd->bound == PDD_BOUND)
>>>              pdd->bound = PDD_BOUND_SUSPENDED;
>>>          mutex_unlock(&p->mutex);
>
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>