linux-kernel - [PATCH AUTOSEL 5.13 057/219] drm/bridge: nwl-dsi: Avoid potential multiplication overflow on 32-bit

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Date:   Thu,  9 Sep 2021 07:43:53 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Fabio Estevam <festevam@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Sasha Levin <sashal@...nel.org>,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 5.13 057/219] drm/bridge: nwl-dsi: Avoid potential multiplication overflow on 32-bit

From: Geert Uytterhoeven <geert+renesas@...der.be>

[ Upstream commit 47956bc86ee4e8530cac386a04f62a6095f7afbe ]

As nwl_dsi.lanes is u32, and NSEC_PER_SEC is 1000000000L, the second
multiplication in

    dsi->lanes * 8 * NSEC_PER_SEC

will overflow on a 32-bit platform.  Fix this by making the constant
unsigned long long, forcing 64-bit arithmetic.

As iMX8 is arm64, this driver is currently used on 64-bit platforms
only, where long is 64-bit, so this cannot happen.  But the issue will
start to happen when the driver is reused for a 32-bit SoC (e.g.
i.MX7ULP), or when code is copied for a new driver.

Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Reviewed-by: Fabio Estevam <festevam@...il.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Sam Ravnborg <sam@...nborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/ebb82941a86b4e35c4fcfb1ef5a5cfad7c1fceab.1626255956.git.geert+renesas@glider.be
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/bridge/nwl-dsi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/nwl-dsi.c b/drivers/gpu/drm/bridge/nwl-dsi.c
index c65ca860712d..6cac2e58cd15 100644
--- a/drivers/gpu/drm/bridge/nwl-dsi.c
+++ b/drivers/gpu/drm/bridge/nwl-dsi.c
@@ -196,7 +196,7 @@ static u32 ps2bc(struct nwl_dsi *dsi, unsigned long long ps)
 	u32 bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
 
 	return DIV64_U64_ROUND_UP(ps * dsi->mode.clock * bpp,
-				  dsi->lanes * 8 * NSEC_PER_SEC);
+				  dsi->lanes * 8ULL * NSEC_PER_SEC);
 }
 
 /*
-- 
2.30.2