linux-hardening - Re: [PATCH] niu: Silence randstruct warnings

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Date:   Wed, 11 May 2022 16:25:11 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>, Du Cheng <ducheng2@...il.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Vlastimil Babka <vbabka@...e.cz>,
        William Kucharski <william.kucharski@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>, netdev@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] niu: Silence randstruct warnings

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@...radead.org>
> > Cc: Christoph Hellwig <hch@...radead.org>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: Jakub Kicinski <kuba@...nel.org>
> > Cc: Paolo Abeni <pabeni@...hat.com>
> > Cc: Du Cheng <ducheng2@...il.com>
> > Cc: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Cc: William Kucharski <william.kucharski@...cle.com>
> > Cc: Arnd Bergmann <arnd@...db.de>
> > Cc: Nathan Chancellor <nathan@...nel.org>
> > Cc: netdev@...r.kernel.org
> > Cc: linux-mm@...ck.org
> > Cc: linux-hardening@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.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@...nel.org>

Thanks!

-- 
Kees Cook