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    Subject[PATCH 5.9 247/757] drm/msm: Avoid div-by-zero in dpu_crtc_atomic_check()
    Date
    From: Stephen Boyd <swboyd@chromium.org>

    [ Upstream commit 22f760941844dbcee6ee446e1896532f6dff01ef ]

    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@codeaurora.org>
    Cc: Jeykumar Sankaran <jsanka@codeaurora.org>
    Cc: Jordan Crouse <jcrouse@codeaurora.org>
    Cc: Sean Paul <seanpaul@chromium.org>
    Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
    Signed-off-by: Stephen Boyd <swboyd@chromium.org>
    Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
    Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
    Signed-off-by: Rob Clark <robdclark@chromium.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
    index c2729f71e2fa7..f9cb1e0da1a59 100644
    --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
    +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
    @@ -881,7 +881,7 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
    struct drm_plane *plane;
    struct drm_display_mode *mode;

    - int cnt = 0, rc = 0, mixer_width, i, z_pos;
    + int cnt = 0, rc = 0, mixer_width = 0, i, z_pos;

    struct dpu_multirect_plane_states multirect_plane[DPU_STAGE_MAX * 2];
    int multirect_count = 0;
    @@ -914,9 +914,11 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,

    memset(pipe_staged, 0, sizeof(pipe_staged));

    - mixer_width = mode->hdisplay / cstate->num_mixers;
    + if (cstate->num_mixers) {
    + mixer_width = mode->hdisplay / cstate->num_mixers;

    - _dpu_crtc_setup_lm_bounds(crtc, state);
    + _dpu_crtc_setup_lm_bounds(crtc, state);
    + }

    crtc_rect.x2 = mode->hdisplay;
    crtc_rect.y2 = mode->vdisplay;
    --
    2.25.1


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