Re: [PATCH v2] drm/nouveau/nvif: Avoid build error due to potential integer overflows

[Kees Cook]

On Sat, May 18, 2024 at 11:29:23AM -0700, Guenter Roeck wrote:
> Trying to build parisc:allmodconfig with gcc 12.x or later results
> in the following build error.
> 
> drivers/gpu/drm/nouveau/nvif/object.c: In function 'nvif_object_mthd':
> drivers/gpu/drm/nouveau/nvif/object.c:161:9: error:
> 	'memcpy' accessing 4294967264 or more bytes at offsets 0 and 32 overlaps 6442450881 bytes at offset -2147483617 [-Werror=restrict]
>   161 |         memcpy(data, args->mthd.data, size);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/nouveau/nvif/object.c: In function 'nvif_object_ctor':
> drivers/gpu/drm/nouveau/nvif/object.c:298:17: error:
> 	'memcpy' accessing 4294967240 or more bytes at offsets 0 and 56 overlaps 6442450833 bytes at offset -2147483593 [-Werror=restrict]
>   298 |                 memcpy(data, args->new.data, size);
> 
> gcc assumes that 'sizeof(*args) + size' can overflow, which would result
> in the problem.
> 
> The problem is not new, only it is now no longer a warning but an error
> since W=1 has been enabled for the drm subsystem and since Werror is
> enabled for test builds.
> 
> Rearrange arithmetic and use check_add_overflow() for validating the
> allocation size to avoid the overflow.
> 
> Fixes: a61ddb4393ad ("drm: enable (most) W=1 warnings by default across the subsystem")
> Cc: Javier Martinez Canillas <javierm@xxxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
> Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> Cc: Maxime Ripard <mripard@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>

Yeah, looks good to me. Thanks!

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook