[PATCH 5.8 207/633] drm/msm: Avoid div-by-zero in dpu_crtc_atomic_check()

Greg Kroah-Hartman
2020-10-27T15:06:42Z

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 1026e1e5bec10..4d81a0c73616f 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