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From:   Walter Harms <wharms@bfs.de>
To:     =?iso-8859-1?Q?Christian_K=F6nig?= <christian.koenig@amd.com>,
        Colin King <colin.king@canonical.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        "David Airlie" <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        Huang Rui <ray.huang@amd.com>,
        Junwei Zhang <Jerry.Zhang@amd.com>,
        "amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
CC:     "kernel-janitors@vger.kernel.org" <kernel-janitors@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: AW: [PATCH] drm/amdgpu: fix potential integer overflow on shift of a
 int
Thread-Topic: [PATCH] drm/amdgpu: fix potential integer overflow on shift of a
 int
Thread-Index: AQHW/aZibC6c7NmnTEaIp1k5r3gR16pN6nEAgAAuR34=
Date:   Mon, 8 Feb 2021 11:05:01 +0000
Message-ID: <3aed86cfb8014badbcbc4ee9f007976d@bfs.de>
References: <20210207230751.8576-1-colin.king@canonical.com>,<c6c99dba-aea9-304c-2246-e24632955479@amd.com>
In-Reply-To: <c6c99dba-aea9-304c-2246-e24632955479@amd.com>
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i am curious:
what is the win to have a unsigned 64 bit integer in the first
place ?

re,
 wh
________________________________________
Von: Christian K=F6nig <christian.koenig@amd.com>
Gesendet: Montag, 8. Februar 2021 10:17:42
An: Colin King; Alex Deucher; David Airlie; Daniel Vetter; Huang Rui; Junwe=
i 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 =3D 31;
...
>         if (*frag >=3D max_frag) {
>                 *frag =3D max_frag;
>                 *frag_end =3D end & ~((1ULL << max_frag) - 1);
>         } else {
>                 *frag_end =3D 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_upd=
ate_params *params,
>               *frag =3D max_frag;
>               *frag_end =3D end & ~((1ULL << max_frag) - 1);
>       } else {
> -             *frag_end =3D start + (1 << *frag);
> +             *frag_end =3D start + (1ULL << *frag);
>       }
>   }
>