linux-kernel - Re: [PATCH] drm/amdgpu/virt: don't dereference undefined 'module' struct

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Date:   Thu, 2 Nov 2017 15:22:05 -0400
From:   Harry Wentland <harry.wentland@....com>
To:     Arnd Bergmann <arnd@...db.de>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Cc:     David Airlie <airlied@...ux.ie>, Horace Chen <horace.chen@....com>,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        Xiangliang Yu <Xiangliang.Yu@....com>,
        dri-devel@...ts.freedesktop.org, Monk Liu <Monk.Liu@....com>
Subject: Re: [PATCH] drm/amdgpu/virt: don't dereference undefined 'module'
 struct

On 2017-11-02 07:25 AM, Arnd Bergmann wrote:
> Accessing the THIS_MODULE directly is only possible when modules
> are enabled, otherwise we get a build failure:
> 
> drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c: In function 'amdgpu_virt_init_data_exchange':
> drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c:331:20: error: dereferencing pointer to incomplete type 'struct module'
> 
> Further, THIS_MODULE is NULL when the driver is built-in, so the
> code would likely cause a NULL pointer dereference.
> 
> This adds an #ifdef check to avoid the compile-time error, plus
> a NULL pointer check before dereferencing THIS_MODULE. It might
> be better to find a way to avoid using the module version
> altogether.
> 
> Fixes: 2dc8f81e4f82 ("drm/amdgpu: SR-IOV data exchange between PF&VF")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Looks like 'str' isn't even used here.

Either way, this change by itself is correct and
Reviewed-by: Harry Wentland <harry.wentland@....com>

Harry

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> index e97f80f86005..4e4a476593e8 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
> @@ -328,9 +328,11 @@ void amdgpu_virt_init_data_exchange(struct amdgpu_device *adev)
>  					sizeof(amdgim_vf2pf_info));
>  				AMDGPU_FW_VRAM_VF2PF_READ(adev, driver_version,
>  					&str);
> +#ifdef MODULE
>  				if (THIS_MODULE->version != NULL)
>  					strcpy(str, THIS_MODULE->version);
>  				else
> +#endif
>  					strcpy(str, "N/A");
>  				AMDGPU_FW_VRAM_VF2PF_WRITE(adev, driver_cert,
>  					0);
>