[PATCH][next] drm/amd/display: Fix potential integer overflow

[PATCH][next] drm/amd/display: Fix potential integer overflow

[Gustavo A. R. Silva]

Fix potential integer overflow by casting actual_calculated_clock_100hz
to u64, in order to give the compiler complete information about the
proper arithmetic to use.

Notice that such variable is used in a context that expects
an expression of type u64 (64 bits, unsigned) and the following
expression is currently being evaluated using 32-bit arithmetic:

actual_calculated_clock_100hz * post_divider

Fixes: 7a03fdf628af ("drm/amd/display: fix 64bit division issue on 32bit OS")
Addresses-Coverity-ID: 1501691 ("Unintentional integer overflow")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
index bc942725b9d8..dec58b3c42e4 100644
--- a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
+++ b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
@@ -240,7 +240,7 @@ static bool calc_fb_divider_checking_tolerance(
 		pll_settings->calculated_pix_clk_100hz =
 			actual_calculated_clock_100hz;
 		pll_settings->vco_freq =
-			div_u64(actual_calculated_clock_100hz * post_divider, 10);
+			div_u64((u64)actual_calculated_clock_100hz * post_divider, 10);
 		return true;
 	}
 	return false;
-- 
2.27.0

Re: [PATCH][next] drm/amd/display: Fix potential integer overflow

[Alex Deucher]

On Wed, Feb 10, 2021 at 4:23 PM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
>
> Fix potential integer overflow by casting actual_calculated_clock_100hz
> to u64, in order to give the compiler complete information about the
> proper arithmetic to use.
>
> Notice that such variable is used in a context that expects
> an expression of type u64 (64 bits, unsigned) and the following
> expression is currently being evaluated using 32-bit arithmetic:
>
> actual_calculated_clock_100hz * post_divider
>
> Fixes: 7a03fdf628af ("drm/amd/display: fix 64bit division issue on 32bit OS")
> Addresses-Coverity-ID: 1501691 ("Unintentional integer overflow")
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Applied.  Thanks!

Alex


> ---
>  drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
> index bc942725b9d8..dec58b3c42e4 100644
> --- a/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
> +++ b/drivers/gpu/drm/amd/display/dc/dce/dce_clock_source.c
> @@ -240,7 +240,7 @@ static bool calc_fb_divider_checking_tolerance(
>                 pll_settings->calculated_pix_clk_100hz =
>                         actual_calculated_clock_100hz;
>                 pll_settings->vco_freq =
> -                       div_u64(actual_calculated_clock_100hz * post_divider, 10);
> +                       div_u64((u64)actual_calculated_clock_100hz * post_divider, 10);
>                 return true;
>         }
>         return false;
> --
> 2.27.0
>
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