Re: [PATCH 1/9] drm/amd/pm: Annotate struct smu10_voltage_dependency_table with __counted_by

[Kees Cook <keescook@xxxxxxxxxxxx>]

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@xxxxxxxxxxxx> 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@xxxxxxx>
> > > Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> > > Cc: "Christian König" <christian.koenig@xxxxxxx>
> > > Cc: "Pan, Xinhui" <Xinhui.Pan@xxxxxxx>
> > > Cc: David Airlie <airlied@xxxxxxxxx>
> > > Cc: Daniel Vetter <daniel@xxxxxxxx>
> > > Cc: Xiaojian Du <Xiaojian.Du@xxxxxxx>
> > > Cc: Huang Rui <ray.huang@xxxxxxx>
> > > Cc: Kevin Wang <kevin1.wang@xxxxxxx>
> > > Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> > > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > Acked-by: Alex Deucher <alexander.deucher@xxxxxxx>
> 
> 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