linux-hardening - Re: [PATCH][next] drm/amd/display: Fix Wstringop-overflow warnings in dc_link

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Date:   Thu, 3 Mar 2022 09:43:28 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/amd/display: Fix Wstringop-overflow warnings
 in dc_link_dp.c

On Thu, Mar 03, 2022 at 11:25:03AM -0600, Gustavo A. R. Silva wrote:
> Fix the following Wstringop-overflow warnings when building with GCC-11:
> 
> drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc_link_dpia.c:493:17: warning: ‘dp_decide_lane_settings’ accessing 4 bytes in a region of size 1 [-Wstringop-overflow=]

Can you "show your work" a little more here? I don't actually see the
what is getting fixed:

enum dc_lane_count {
	...
        LANE_COUNT_FOUR = 4,
	...
        LANE_COUNT_DP_MAX = LANE_COUNT_FOUR
};

struct link_training_settings {
	...
        union dpcd_training_lane dpcd_lane_settings[LANE_COUNT_DP_MAX];
};

void dp_hw_to_dpcd_lane_settings(
		...
		union dpcd_training_lane dpcd_lane_settings[LANE_COUNT_DP_MAX])
{
	...
}

static enum link_training_result dpia_training_cr_transparent(
		...
                struct link_training_settings *lt_settings)
{
	...
                dp_decide_lane_settings(lt_settings, dpcd_lane_adjust,
                                lt_settings->hw_lane_settings, lt_settings->dpcd_lane_settings);
	...
}

Everything looks to be the correct size?

-- 
Kees Cook