linux-kernel - Re: [PATCH] drm/amdgpu: Fixes uninitialized variable usage in amdgpu_dm_setup

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Date:   Fri, 27 Oct 2023 11:53:52 -0400
From:   Hamza Mahfooz <hamza.mahfooz@....com>
To:     Yuran Pereira <yuran.pereira@...mail.com>, airlied@...il.com
Cc:     sunpeng.li@....com, linux-kernel-mentees@...ts.linuxfoundation.org,
        Xinhui.Pan@....com, Rodrigo.Siqueira@....com,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, alexander.deucher@....com,
        Bhawanpreet.Lakha@....com, christian.koenig@....com
Subject: Re: [PATCH] drm/amdgpu: Fixes uninitialized variable usage in
 amdgpu_dm_setup_replay

Also, please write the tagline in present tense.
On 10/27/23 11:53, Hamza Mahfooz wrote:
> 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@...mail.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