Re: [PATCH] niu: Silence randstruct warnings

Kees Cook
2022-05-11T23:25:23Z

On Wed, May 11, 2022 at 03:16:47PM -0700, Jakub Kicinski wrote:
> On Tue, 10 May 2022 13:57:29 -0700 Kees Cook wrote:
> > Clang randstruct gets upset when it sees struct addresspace (which is
> > randomized) being assigned to a struct page (which is not randomized):
> >
> > drivers/net/ethernet/sun/niu.c:3385:12: error: casting from randomized structure pointer type 'struct address_space *' to 'struct page *'
> > *link = (struct page *) page->mapping;
> > ^
> >
> > It looks like niu.c is looking for an in-line place to chain its allocated
> > pages together and is overloading the "mapping" member, as it is unused.
> > This is very non-standard, and is expected to be cleaned up in the
> > future[1], but there is no "correct" way to handle it today.
> >
> > No meaningful machine code changes result after this change, and source
> > readability is improved.
> >
> > Drop the randstruct exception now that there is no "confusing" cross-type
> > assignment.
> >
> > [1] https://lore.kernel.org/lkml/YnqgjVoMDu5v9PNG@casper.infradead.org/
> >
> > Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > Cc: Christoph Hellwig <hch@infradead.org>
> > Cc: "David S. Miller" <davem@davemloft.net>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Paolo Abeni <pabeni@redhat.com>
> > Cc: Du Cheng <ducheng2@gmail.com>
> > Cc: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: William Kucharski <william.kucharski@oracle.com>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Nathan Chancellor <nathan@kernel.org>
> > Cc: netdev@vger.kernel.org
> > Cc: linux-mm@kvack.org
> > Cc: linux-hardening@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
>
> I presume you prefer to take this one via your tree too, so:

Yeah, that's easiest for the exception removals.

> Acked-by: Jakub Kicinski <kuba@kernel.org>

Thanks!

--
Kees Cook