linux-kernel - Re: [PATCH] drm/vmwgfx: Fix uninitialized use of dst_pitch in vmw_stdu_bo_cpu

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Message-ID: <0d916c098eccdb28db352f7fa01cd401895c734f.camel@vmware.com>
Date:   Tue, 14 Mar 2023 21:13:24 +0000
From:   Zack Rusin <zackr@...are.com>
To:     "nathan@...nel.org" <nathan@...nel.org>
CC:     "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        Maaz Mombasawala <mombasawalam@...are.com>,
        "tzimmermann@...e.de" <tzimmermann@...e.de>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Martin Krastev <krastevm@...are.com>,
        "trix@...hat.com" <trix@...hat.com>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        Linux-graphics-maintainer <Linux-graphics-maintainer@...are.com>
Subject: Re: [PATCH] drm/vmwgfx: Fix uninitialized use of dst_pitch in
 vmw_stdu_bo_cpu_commit()

On Tue, 2023-03-14 at 08:38 -0700, Nathan Chancellor wrote:
> Clang warns (or errors with CONFIG_WERROR):
> 
>   drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c:509:29: error: variable 'dst_pitch' is
> uninitialized when used here [-Werror,-Wuninitialized]
>           src_offset = ddirty->top * dst_pitch + ddirty->left * stdu->cpp;
>                                      ^~~~~~~~~
>   drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c:492:26: note: initialize the variable
> 'dst_pitch' to silence this warning
>           s32 src_pitch, dst_pitch;
>                                   ^
>                                    = 0
>   1 error generated.
> 
> The assignments were switched around in such a way that dst_pitch was
> used before it was assigned. Swap the pitch assignments to fix the issue
> and make it clear which section they are used in.
> 
> Fixes: 39985eea5a6d ("drm/vmwgfx: Abstract placement selection")
> Link:
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FClangBuiltLinux%2Flinux%2Fissues%2F1811&data=05%7C01%7Czackr%40vmware.com%7C37398ac97246436c2efc08db24a226d5%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C638144051125910171%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=HtZTNLdmCAzHfRoEG6vsWcSul4YRSZ56BO2ZUHnUCj4%3D&reserved=0
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> I am not sure if this is the right fix, as it was not entirely clear to
> me that src_pitch and dst_pitch were being used in the right assignments
> but this is the obvious fix otherwise. Consider this a bug report if
> not :)
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> b/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> index d79a6eccfaa4..030e977c68e2 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c
> @@ -504,11 +504,11 @@ static void vmw_stdu_bo_cpu_commit(struct vmw_kms_dirty
> *dirty)
>                 return;
>  
>         /* Assume we are blitting from Guest (bo) to Host (display_srf) */
> -       src_pitch = stdu->display_srf->metadata.base_size.width * stdu->cpp;
> +       dst_pitch = ddirty->pitch;
>         src_bo = &stdu->display_srf->res.guest_memory_bo->tbo;
>         src_offset = ddirty->top * dst_pitch + ddirty->left * stdu->cpp;
>  
> -       dst_pitch = ddirty->pitch;
> +       src_pitch = stdu->display_srf->metadata.base_size.width * stdu->cpp;
>         dst_bo = &ddirty->buf->tbo;
>         dst_offset = ddirty->fb_top * src_pitch + ddirty->fb_left * stdu->cpp;

Thanks Nathan! In this case we just want to switch the usage instead of what those
variables are. I'll send a patch out in a second.

z