Re: [PATCH] drm/amdgpu: Fixes uninitialized variable usage in amdgpu_dm_setup_replay

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 28.10.23 um 02:48 schrieb Yuran Pereira:
> Hello,
> On Fri, Oct 27, 2023 at 11:57:45AM -0400, Hamza Mahfooz wrote:
>> On 10/27/23 11:55, Lakha, Bhawanpreet wrote:
>>> [AMD Official Use Only - General]
>>>
>>>
>>>
>>> There was a consensus to use memset instead of {0}. I remember making
>>> changes related to that previously.
>> Hm, seems like it's used rather consistently in the DM and in DC
>> though.
>>
> Have you decided which one should be used?
>
> Should I submit a v2 patch using {0} instead of memset?

The problem is that {0} doesn't initialize padding fields in structures.

So what can happen are problems like leaking bytes to userspace or 
getting unstable hash keys etc...

So I think memset() is usually preferred and that not only counts for Linux.

Regards,
Christian.

>
>
> Yuran Pereira
>>> Bhawan
>>>
>>> ------------------------------------------------------------------------
>>> *From:* Mahfooz, Hamza <Hamza.Mahfooz@amd.com>
>>> *Sent:* October 27, 2023 11:53 AM
>>> *To:* Yuran Pereira <yuran.pereira@hotmail.com>; airlied@gmail.com
>>> <airlied@gmail.com>
>>> *Cc:* Li, Sun peng (Leo) <Sunpeng.Li@amd.com>; Lakha, Bhawanpreet
>>> <Bhawanpreet.Lakha@amd.com>; Pan, Xinhui <Xinhui.Pan@amd.com>; Siqueira,
>>> Rodrigo <Rodrigo.Siqueira@amd.com>; linux-kernel@vger.kernel.org
>>> <linux-kernel@vger.kernel.org>; amd-gfx@lists.freedesktop.org
>>> <amd-gfx@lists.freedesktop.org>; dri-devel@lists.freedesktop.org
>>> <dri-devel@lists.freedesktop.org>; Deucher, Alexander
>>> <Alexander.Deucher@amd.com>; Koenig, Christian
>>> <Christian.Koenig@amd.com>;
>>> linux-kernel-mentees@lists.linuxfoundation.org
>>> <linux-kernel-mentees@lists.linuxfoundation.org>
>>> *Subject:* Re: [PATCH] drm/amdgpu: Fixes uninitialized variable usage in
>>> amdgpu_dm_setup_replay
>>> On 10/26/23 17:25, Yuran Pereira wrote:
>>>> Since `pr_config` is not initialized after its declaration, the
>>>> following operations with `replay_enable_option` may be performed
>>>> when `replay_enable_option` is holding junk values which could
>>>> possibly lead to undefined behaviour
>>>>
>>>> ```
>>>>        ...
>>>>        pr_config.replay_enable_option |= pr_enable_option_static_screen;
>>>>        ...
>>>>
>>>>        if (!pr_config.replay_timing_sync_supported)
>>>>            pr_config.replay_enable_option &= ~pr_enable_option_general_ui;
>>>>        ...
>>>> ```
>>>>
>>>> This patch initializes `pr_config` after its declaration to ensure that
>>>> it doesn't contain junk data, and prevent any undefined behaviour
>>>>
>>>> Addresses-Coverity-ID: 1544428 ("Uninitialized scalar variable")
>>>> Fixes: dede1fea4460 ("drm/amd/display: Add Freesync Panel DM code")
>>>> Signed-off-by: Yuran Pereira <yuran.pereira@hotmail.com>
>>>> ---
>>>>     drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_replay.c | 3 +++
>>>>     1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_replay.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_replay.c
>>>> index 32d3086c4cb7..40526507f50b 100644
>>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_replay.c
>>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_replay.c
>>>> @@ -23,6 +23,7 @@
>>>>      *
>>>>      */
>>>> +#include <linux/string.h>
>>>>     #include "amdgpu_dm_replay.h"
>>>>     #include "dc.h"
>>>>     #include "dm_helpers.h"
>>>> @@ -74,6 +75,8 @@ bool amdgpu_dm_setup_replay(struct dc_link *link, struct amdgpu_dm_connector *ac
>>>>          struct replay_config pr_config;
>>> I would prefer setting pr_config = {0};
>>>
>>>>          union replay_debug_flags *debug_flags = NULL;
>>>> +     memset(&pr_config, 0, sizeof(pr_config));
>>>> +
>>>>          // For eDP, if Replay is supported, return true to skip checks
>>>>          if (link->replay_settings.config.replay_supported)
>>>>                  return true;
>>> -- 
>>> Hamza
>>>
>> -- 
>> Hamza
>>