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SubjectRe: [PATCH] drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64 result
On Tue, Sep 15, 2020 at 9:20 AM Colin King <colin.king@canonical.com> wrote:
>
> 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>

Reviewed-by: Guenter Roeck <groeck@chromium.org>

> ---
> 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
>

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