Subject: Re: [PATCH] drm/amdkfd: Fix potential NULL pointer dereferences
To: "Gustavo A. R. Silva" <garsilva@embeddedor.com>,
        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>
Cc: amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <20180110165008.GA10691@embeddedor.com>
From: Felix Kuehling <felix.kuehling@amd.com>
Organization: AMD Inc.
Message-ID: <c4197e6a-ba58-23b9-8fa8-8a9b3ff74ef9@amd.com>
Date: Wed, 10 Jan 2018 13:33:20 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.5.0
MIME-Version: 1.0
In-Reply-To: <20180110165008.GA10691@embeddedor.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Content-Language: en-CA
SpamDiagnosticOutput: 1:99
SpamDiagnosticMetadata: NSPM
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Jan 2018 18:33:23.8679 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 4cb0d3e9-42d4-4e91-c162-08d55858a252
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR1201MB0235
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

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.

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);