linux-kernel - Re: [PATCH] drm/msm/dpu: change _dpu_plane_calc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Fri, 8 Sep 2023 03:54:55 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Kalyan Thota <quic_kalyant@...cinc.com>
Cc:     dri-devel@...ts.freedesktop.org, quic_jesszhan@...cinc.com,
        quic_parellan@...cinc.com, nespera@...lia.com,
        Rob Clark <robdclark@...omium.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dpu: change _dpu_plane_calc_bw() to use u64 to
 avoid overflow

On 08/09/2023 03:52, Abhinav Kumar wrote:
> 
> 
> On 9/7/2023 5:35 PM, Dmitry Baryshkov wrote:
>> On 08/09/2023 03:32, Abhinav Kumar wrote:
>>> _dpu_plane_calc_bw() uses integer variables to calculate the bandwidth
>>> used during plane bandwidth calculations. However for high resolution
>>> displays this overflows easily and leads to below errors
>>
>> Can we move the u64 conversion closer to the place where we actually 
>> need it? Having u64 source width looks very strange.
>>
> 
> Its this math 
> https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c#L139 which overflows.
> 
> So its not just one variable but I can even change this to u32 as that 
> also fixes the issue. Let me know if u32 works better.
> 
> Perhaps I went too far to go from int to u64.

I'd prefer to have the u64 conversion around the actual calculations - 
so that we emphasise the issue, not the size of the width / etc.

> 
>>>
>>> [dpu error]crtc83 failed performance check -7
>>>
>>> Promote the intermediate variables to u64 to avoid overflow.
>>>
>>> Fixes: c33b7c0389e1 ("drm/msm/dpu: add support for clk and bw scaling 
>>> for display")
>>> Closes: https://gitlab.freedesktop.org/drm/msm/-/issues/32
>>> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
>>> ---
>>>   drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c 
>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
>>> index ae970af1154f..c6193131beec 100644
>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
>>> @@ -118,7 +118,7 @@ static u64 _dpu_plane_calc_bw(const struct 
>>> dpu_mdss_cfg *catalog,
>>>       const struct drm_display_mode *mode,
>>>       struct dpu_sw_pipe_cfg *pipe_cfg)
>>>   {
>>> -    int src_width, src_height, dst_height, fps;
>>> +    u64 src_width, src_height, dst_height, fps;
>>>       u64 plane_prefill_bw;
>>>       u64 plane_bw;
>>>       u32 hw_latency_lines;
>>

-- 
With best wishes
Dmitry