From: Colin King <colin.king@canonical.com>
To: "Sandy Huang" <hjc@rock-chips.com>,
"Heiko Stübner" <heiko@sntech.de>,
"David Airlie" <airlied@linux.ie>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Chris Zhong" <zyw@rock-chips.com>,
"Guenter Roeck" <groeck@chromium.org>,
"Sean Paul" <seanpaul@chromium.org>,
dri-devel@lists.freedesktop.org,
linux-arm-kernel@lists.infradead.org,
linux-rockchip@lists.infradead.org
Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64 result
Date: Tue, 15 Sep 2020 17:20:49 +0100 [thread overview]
Message-ID: <20200915162049.36434-1-colin.king@canonical.com> (raw)
From: Colin Ian King <colin.king@canonical.com>
The variable bit_per_pix is a u8 and is promoted in the multiplication
to an int type and then sign extended to a u64. If the result of the
int multiplication is greater than 0x7fffffff then the upper 32 bits will
be set to 1 as a result of the sign extension. Avoid this by casting
tu_size_reg to u64 to avoid sign extension and also a potential overflow.
Addresses-Coverity: ("Unintended sign extension")
Fixes: 1a0f7ed3abe2 ("drm/rockchip: cdn-dp: add cdn DP support for rk3399")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
drivers/gpu/drm/rockchip/cdn-dp-reg.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/rockchip/cdn-dp-reg.c b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
index 9d2163ef4d6e..33fb4d05c506 100644
--- a/drivers/gpu/drm/rockchip/cdn-dp-reg.c
+++ b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
@@ -658,7 +658,7 @@ int cdn_dp_config_video(struct cdn_dp_device *dp)
*/
do {
tu_size_reg += 2;
- symbol = tu_size_reg * mode->clock * bit_per_pix;
+ symbol = (u64)tu_size_reg * mode->clock * bit_per_pix;
do_div(symbol, dp->max_lanes * link_rate * 8);
rem = do_div(symbol, 1000);
if (tu_size_reg > 64) {
--
2.27.0
next reply other threads:[~2020-09-15 22:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 16:20 Colin King [this message]
2020-09-15 17:29 ` [PATCH] drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64 result Guenter Roeck
2021-05-28 18:55 ` Heiko Stuebner
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