linux-kernel - [PATCH] drm/msm/dpu: Fix bit-shifting UB in DPU_HW

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Message-Id: <20230306090633.65918-1-geert+renesas@glider.be>
Date:   Mon,  6 Mar 2023 10:06:33 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc:     linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] drm/msm/dpu: Fix bit-shifting UB in DPU_HW_VER() macro

With gcc-5 and CONFIG_UBSAN_SHIFT=y:

    drivers/gpu/drm/msm/msm_mdss.c: In function 'msm_mdss_enable':
    drivers/gpu/drm/msm/msm_mdss.c:296:2: error: case label does not reduce to an integer constant
      case DPU_HW_VER_800:
      ^
    drivers/gpu/drm/msm/msm_mdss.c:299:2: error: case label does not reduce to an integer constant
      case DPU_HW_VER_810:
      ^
    drivers/gpu/drm/msm/msm_mdss.c:300:2: error: case label does not reduce to an integer constant
      case DPU_HW_VER_900:
      ^

This happens because for major revisions 8 or greather, the non-sign bit
of the major revision number is shifted into bit 31 of a signed integer,
which is undefined behavior.

Fix this by casting the major revision number to unsigned int.

Fixes: efcd0107727c4f04 ("drm/msm/dpu: add support for SM8550")
Fixes: 4a352c2fc15aec1e ("drm/msm/dpu: Introduce SC8280XP")
Fixes: 100d7ef6995d1f86 ("drm/msm/dpu: add support for SM8450")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
index ddab9caebb18c40d..bbd3cbdd77956c5d 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
@@ -19,8 +19,9 @@
  */
 #define MAX_BLOCKS    12
 
-#define DPU_HW_VER(MAJOR, MINOR, STEP) (((MAJOR & 0xF) << 28)    |\
-		((MINOR & 0xFFF) << 16)  |\
+#define DPU_HW_VER(MAJOR, MINOR, STEP)			\
+		((((unsigned int)MAJOR & 0xF) << 28) |	\
+		((MINOR & 0xFFF) << 16) |		\
 		(STEP & 0xFFFF))
 
 #define DPU_HW_MAJOR(rev)		((rev) >> 28)
-- 
2.34.1