linux-kernel - Re: [PATCH v2] drm/ttm: Silence randstruct warning about casting struct file

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <202505011922.04F401E@keescook>
Date: Thu, 1 May 2025 19:24:30 -0700
From: Kees Cook <kees@...nel.org>
To: Matthew Brost <matthew.brost@...el.com>
Cc: Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
	Christian Koenig <christian.koenig@....com>,
	Somalapuram Amaranath <Amaranath.Somalapuram@....com>,
	Huang Rui <ray.huang@....com>,
	Matthew Auld <matthew.auld@...el.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] drm/ttm: Silence randstruct warning about casting
 struct file

On Thu, May 01, 2025 at 07:13:12PM -0700, Matthew Brost wrote:
> On Thu, May 01, 2025 at 05:24:38PM -0700, Kees Cook wrote:
> > Casting through a "void *" isn't sufficient to convince the randstruct
> > GCC plugin that the result is intentional. Instead operate through an
> > explicit union to silence the warning:
> > 
> > drivers/gpu/drm/ttm/ttm_backup.c: In function 'ttm_file_to_backup':
> > drivers/gpu/drm/ttm/ttm_backup.c:21:16: note: randstruct: casting between randomized structure pointer types (ssa): 'struct ttm_backup' and 'struct file'
> >    21 |         return (void *)file;
> >       |                ^~~~~~~~~~~~
> > 
> > Suggested-by: Matthew Brost <matthew.brost@...el.com>
> 
> I forgot the policy if suggest-by but will add:
> Reviewed-by: Matthew Brost <matthew.brost@...el.com>

Yeah, and feel free to snag authorship entirely if you want. I only
updated the comment, really. :)

> Thomas was out today I suspect he will look at this tomorrow when he is
> back too.

Cool, no rush. It's currently just a warning in -next re-exposed by
randstruct getting cleared for allmodconfig again. :)

Thanks!

-Kees

-- 
Kees Cook