Re: [PATCH] drm/amdgpu: Avoid possible buffer overflow

[Christophe JAILLET]

Le 21/08/2023 à 08:19, Su Hui a écrit :
> smatch error:
> drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1257 amdgpu_discovery_reg_base_init() error:
> testing array offset 'adev->vcn.num_vcn_inst' after use.
>
> change the assignment order to avoid buffer overflow.
>
> Fixes: c40bdfb2ffa4 ("drm/amdgpu: fix incorrect VCN revision in SRIOV")
> Signed-off-by: Su Hui <suhui@xxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
> index 8e1cfc87122d..ba95526c3d45 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
> @@ -1250,11 +1250,12 @@ static int amdgpu_discovery_reg_base_init(struct amdgpu_device *adev)
>   				 *     0b10 : encode is disabled
>   				 *     0b01 : decode is disabled
>   				 */
> -				adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
> -					ip->revision & 0xc0;
> +
>   				ip->revision &= ~0xc0;
>   				if (adev->vcn.num_vcn_inst <
>   				    AMDGPU_MAX_VCN_INSTANCES) {
> +					adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
> +						ip->revision & 0xc0;

Hi,
I don't think that the patch is correct.

Because of the "ip->revision &= ~0xc0" which is now above it, 
"ip->revision & 0xc0" should now always be 0.

Maybe both lines should be moved within the "if"?

CJ





>   					adev->vcn.num_vcn_inst++;
>   					adev->vcn.inst_mask |=
>   						(1U << ip->instance_number);