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

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Date:   Fri, 27 Oct 2023 11:53:06 -0400
From:   Hamza Mahfooz <hamza.mahfooz@....com>
To:     Yuran Pereira <yuran.pereira@...mail.com>, airlied@...il.com
Cc:     sunpeng.li@....com, Bhawanpreet.Lakha@....com, Xinhui.Pan@....com,
        Rodrigo.Siqueira@....com, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        alexander.deucher@....com, christian.koenig@....com,
        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