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

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Message-ID: <39ab34ec-209d-4176-b271-1a02e2976497@amd.com>
Date:   Fri, 27 Oct 2023 11:57:45 -0400
From:   Hamza Mahfooz <hamza.mahfooz@....com>
To:     "Lakha, Bhawanpreet" <Bhawanpreet.Lakha@....com>,
        Yuran Pereira <yuran.pereira@...mail.com>,
        "airlied@...il.com" <airlied@...il.com>
Cc:     "Li, Sun peng (Leo)" <Sunpeng.Li@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        "Siqueira, Rodrigo" <Rodrigo.Siqueira@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        "linux-kernel-mentees@...ts.linuxfoundation.org" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [PATCH] drm/amdgpu: Fixes uninitialized variable usage in
 amdgpu_dm_setup_replay

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.

> 
> Bhawan
> 
> ------------------------------------------------------------------------
> *From:* Mahfooz, Hamza <Hamza.Mahfooz@....com>
> *Sent:* October 27, 2023 11:53 AM
> *To:* Yuran Pereira <yuran.pereira@...mail.com>; airlied@...il.com 
> <airlied@...il.com>
> *Cc:* Li, Sun peng (Leo) <Sunpeng.Li@....com>; Lakha, Bhawanpreet 
> <Bhawanpreet.Lakha@....com>; Pan, Xinhui <Xinhui.Pan@....com>; Siqueira, 
> Rodrigo <Rodrigo.Siqueira@....com>; linux-kernel@...r.kernel.org 
> <linux-kernel@...r.kernel.org>; amd-gfx@...ts.freedesktop.org 
> <amd-gfx@...ts.freedesktop.org>; dri-devel@...ts.freedesktop.org 
> <dri-devel@...ts.freedesktop.org>; Deucher, Alexander 
> <Alexander.Deucher@....com>; Koenig, Christian 
> <Christian.Koenig@....com>; 
> linux-kernel-mentees@...ts.linuxfoundation.org 
> <linux-kernel-mentees@...ts.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@...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
> 
-- 
Hamza