linux-hardening - Re: [PATCH 1/9] drm/amd/pm: Annotate struct smu10_voltage_dependency_table with __counted

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Message-ID: <CADnq5_PaXmFa6N_2-NRp7_2+m3TYt8s--4aYm1UTnQKXDUhwYw@mail.gmail.com>
Date: Mon, 25 Sep 2023 13:56:16 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Kees Cook <keescook@...omium.org>
Cc: Christian König <christian.koenig@....com>, 
	David Airlie <airlied@...il.com>, Tejas Upadhyay <tejas.upadhyay@...el.com>, 
	Emma Anholt <emma@...olt.net>, Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev, 
	dri-devel@...ts.freedesktop.org, Chris Wilson <chris@...is-wilson.co.uk>, 
	Prike Liang <Prike.Liang@....com>, Huang Rui <ray.huang@....com>, 
	Gerd Hoffmann <kraxel@...hat.com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, Matthew Brost <matthew.brost@...el.com>, 
	Karol Herbst <kherbst@...hat.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	amd-gfx@...ts.freedesktop.org, Kuogee Hsieh <quic_khsieh@...cinc.com>, 
	Nathan Chancellor <nathan@...nel.org>, 
	VMware Graphics Reviewers <linux-graphics-maintainer@...are.com>, Ben Skeggs <bskeggs@...hat.com>, 
	Andi Shyti <andi.shyti@...ux.intel.com>, nouveau@...ts.freedesktop.org, 
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	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, Gurchetan Singh <gurchetansingh@...omium.org>, 
	Maxime Ripard <mripard@...nel.org>, Rodrigo Vivi <rodrigo.vivi@...el.com>, 
	Evan Quan <evan.quan@....com>, Sean Paul <sean@...rly.run>, 
	Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>, Xiaojian Du <Xiaojian.Du@....com>, 
	Le Ma <le.ma@....com>, freedreno@...ts.freedesktop.org, 
	Bjorn Andersson <andersson@...nel.org>, "Pan, Xinhui" <Xinhui.Pan@....com>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, linux-kernel@...r.kernel.org, 
	Alex Deucher <alexander.deucher@....com>, Nirmoy Das <nirmoy.das@...el.com>, 
	Lang Yu <Lang.Yu@....com>, John Harrison <john.c.harrison@...el.com>, 
	Hawking Zhang <Hawking.Zhang@....com>
Subject: Re: [PATCH 1/9] drm/amd/pm: Annotate struct smu10_voltage_dependency_table
 with __counted_by

On Mon, Sep 25, 2023 at 1:52 PM Kees Cook <keescook@...omium.org> wrote:
>
> On Mon, Sep 25, 2023 at 08:30:30AM +0200, Christian König wrote:
> > Am 22.09.23 um 19:41 schrieb Alex Deucher:
> > > On Fri, Sep 22, 2023 at 1:32 PM Kees Cook <keescook@...omium.org> wrote:
> > > > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > > > attribute. Flexible array members annotated with __counted_by can have
> > > > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> > > > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > > > functions).
> > > >
> > > > As found with Coccinelle[1], add __counted_by for struct smu10_voltage_dependency_table.
> > > >
> > > > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> > > >
> > > > Cc: Evan Quan <evan.quan@....com>
> > > > Cc: Alex Deucher <alexander.deucher@....com>
> > > > Cc: "Christian König" <christian.koenig@....com>
> > > > Cc: "Pan, Xinhui" <Xinhui.Pan@....com>
> > > > Cc: David Airlie <airlied@...il.com>
> > > > Cc: Daniel Vetter <daniel@...ll.ch>
> > > > Cc: Xiaojian Du <Xiaojian.Du@....com>
> > > > Cc: Huang Rui <ray.huang@....com>
> > > > Cc: Kevin Wang <kevin1.wang@....com>
> > > > Cc: amd-gfx@...ts.freedesktop.org
> > > > Cc: dri-devel@...ts.freedesktop.org
> > > > Signed-off-by: Kees Cook <keescook@...omium.org>
> > > Acked-by: Alex Deucher <alexander.deucher@....com>
> >
> > Mhm, I'm not sure if this is a good idea. That is a structure filled in by
> > the firmware, isn't it?
> >
> > That would imply that we might need to byte swap count before it is
> > checkable.
>
> The script found this instance because of this:
>
> static int smu10_get_clock_voltage_dependency_table(struct pp_hwmgr *hwmgr,
>                         struct smu10_voltage_dependency_table **pptable,
>                         uint32_t num_entry, const DpmClock_t *pclk_dependency_table)
> {
>         uint32_t i;
>         struct smu10_voltage_dependency_table *ptable;
>
>         ptable = kzalloc(struct_size(ptable, entries, num_entry), GFP_KERNEL);
>         if (NULL == ptable)
>                 return -ENOMEM;
>
>         ptable->count = num_entry;
>
> So the implication is that it's native byte order... but you tell me! I
> certainly don't want this annotation if it's going to break stuff. :)

In this case, the code is for an integrated GPU in an x86 CPU so the
firmware and driver endianness match.  You wouldn't find a stand alone
dGPU that uses this structure.  In this case it's ok.  False alarm.

Alex