AW: [PATCH] drm/amdgpu: fix potential integer overflow on shift of a int

[Walter Harms <wharms@bfs.de>]

i am curious:
what is the win to have a unsigned 64 bit integer in the first
place ?

re,
 wh
________________________________________
Von: Christian König <christian.koenig@amd.com>
Gesendet: Montag, 8. Februar 2021 10:17:42
An: Colin King; Alex Deucher; David Airlie; Daniel Vetter; Huang Rui; Junwei Zhang; amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
Cc: kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org
Betreff: Re: [PATCH] drm/amdgpu: fix potential integer overflow on shift of a int

Am 08.02.21 um 00:07 schrieb Colin King:
> From: Colin Ian King <colin.king@canonical.com>
>
> The left shift of int 32 bit integer constant 1 is evaluated using 32
> bit arithmetic and then assigned to an unsigned 64 bit integer. In the
> case where *frag is 32 or more this can lead to an oveflow.  Avoid this
> by shifting 1ULL.

Well that can't happen. Take a look at the code in that function:

>                 max_frag = 31;
...
>         if (*frag >= max_frag) {
>                 *frag = max_frag;
>                 *frag_end = end & ~((1ULL << max_frag) - 1);
>         } else {
>                 *frag_end = start + (1 << *frag);
>         }

But I'm fine with applying the patch if it silences your warning.

Regards,
Christian.

>
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: dfcd99f6273e ("drm/amdgpu: meld together VM fragment and huge page handling")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> index 9d19078246c8..53a925600510 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
> @@ -1412,7 +1412,7 @@ static void amdgpu_vm_fragment(struct amdgpu_vm_update_params *params,
>               *frag = max_frag;
>               *frag_end = end & ~((1ULL << max_frag) - 1);
>       } else {
> -             *frag_end = start + (1 << *frag);
> +             *frag_end = start + (1ULL << *frag);
>       }
>   }
>