linux-kernel - Re: [PATCH 1/2] drm/msm: Avoid div-by-zero in dpu_crtc_atomic

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Date:   Wed, 02 Sep 2020 12:35:30 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Rob Clark <robdclark@...il.com>, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Jeykumar Sankaran <jsanka@...eaurora.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Sean Paul <seanpaul@...omium.org>,
        linux-arm-msm-owner@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/msm: Avoid div-by-zero in dpu_crtc_atomic_check()

On 2020-09-02 03:29, Stephen Boyd wrote:
> The cstate->num_mixers member is only set to a non-zero value once
> dpu_encoder_virt_mode_set() is called, but the atomic check function 
> can
> be called by userspace before that. Let's avoid the div-by-zero here 
> and
> inside _dpu_crtc_setup_lm_bounds() by skipping this part of the atomic
> check if dpu_encoder_virt_mode_set() hasn't been called yet. This fixes
> an UBSAN warning:
> 
>  UBSAN: Undefined behaviour in 
> drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c:860:31
>  division by zero
>  CPU: 7 PID: 409 Comm: frecon Tainted: G S                5.4.31 #128
>  Hardware name: Google Trogdor (rev0) (DT)
>  Call trace:
>   dump_backtrace+0x0/0x14c
>   show_stack+0x20/0x2c
>   dump_stack+0xa0/0xd8
>   __ubsan_handle_divrem_overflow+0xec/0x110
>   dpu_crtc_atomic_check+0x97c/0x9d4
>   drm_atomic_helper_check_planes+0x160/0x1c8
>   drm_atomic_helper_check+0x54/0xbc
>   drm_atomic_check_only+0x6a8/0x880
>   drm_atomic_commit+0x20/0x5c
>   drm_atomic_helper_set_config+0x98/0xa0
>   drm_mode_setcrtc+0x308/0x5dc
>   drm_ioctl_kernel+0x9c/0x114
>   drm_ioctl+0x2ac/0x4b0
>   drm_compat_ioctl+0xe8/0x13c
>   __arm64_compat_sys_ioctl+0x184/0x324
>   el0_svc_common+0xa4/0x154
>   el0_svc_compat_handler+0x
> 
> Cc: Abhinav Kumar <abhinavk@...eaurora.org>
> Cc: Jeykumar Sankaran <jsanka@...eaurora.org>
> Cc: Jordan Crouse <jcrouse@...eaurora.org>
> Cc: Sean Paul <seanpaul@...omium.org>
> Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>

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