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

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Date: Mon, 25 Sep 2023 10:52:33 -0700
From: Kees Cook <keescook@...omium.org>
To: Christian König <christian.koenig@....com>
Cc: Alex Deucher <alexdeucher@...il.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,
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	Prike Liang <Prike.Liang@....com>, Huang Rui <ray.huang@....com>,
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	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>,
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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 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. :)

-- 
Kees Cook