linux-hardening - Re: [PATCH 25/64] drm/mga/mga_ioc32: Use struct

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Message-ID: <202107302118.C0B84E521@keescook>
Date:   Fri, 30 Jul 2021 21:20:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kbuild@...r.kernel.org, netdev@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-wireless@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-block@...r.kernel.org, clang-built-linux@...glegroups.com,
        Keith Packard <keithpac@...zon.com>,
        linux-hardening@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 25/64] drm/mga/mga_ioc32: Use struct_group() for memcpy()
 region

On Thu, Jul 29, 2021 at 02:11:27PM +0200, Daniel Vetter wrote:
> On Wed, Jul 28, 2021 at 07:56:40AM +0200, Greg Kroah-Hartman wrote:
> > On Tue, Jul 27, 2021 at 01:58:16PM -0700, Kees Cook wrote:
> > > In preparation for FORTIFY_SOURCE performing compile-time and run-time
> > > field bounds checking for memcpy(), memmove(), and memset(), avoid
> > > intentionally writing across neighboring fields.
> > > 
> > > Use struct_group() in struct drm32_mga_init around members chipset, sgram,
> > > maccess, fb_cpp, front_offset, front_pitch, back_offset, back_pitch,
> > > depth_cpp, depth_offset, depth_pitch, texture_offset, and texture_size,
> > > so they can be referenced together. This will allow memcpy() and sizeof()
> > > to more easily reason about sizes, improve readability, and avoid future
> > > warnings about writing beyond the end of chipset.
> > > 
> > > "pahole" shows no size nor member offset changes to struct drm32_mga_init.
> > > "objdump -d" shows no meaningful object code changes (i.e. only source
> > > line number induced differences and optimizations).
> > > 
> > > Note that since this includes a UAPI header, struct_group() has been
> > > explicitly redefined local to the header.
> > > [...]
> > 
> > Why can you use __struct_group in this uapi header, but not the
> > networking one?
> 
> If there's others, maybe we can stuff the uapi __struct_group into
> linux/types.h where all the other __ uapi types hang out?

Ah yeah; it looks like include/uapi/linux/stddef.h is the place for it.

> Anyway mga is very dead, I don't anyone cares.
> 
> Acked-by: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> I'm assuming this goes in through a topic pull from you?

Thanks! Yeah, my intention is to carry this as topic branch for Linus.

-Kees

-- 
Kees Cook