Re: [RFC PATCH 2/2] mmc: renesas_sdhi: prevent overflow for max_req_size

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Hi Wolfram,

On Fri, Mar 15, 2019 at 10:39 AM Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote:
> > > I am still confused. Which upper limit do you mean then? Because for
> >
> > TMIO_MAX_BLK_SIZE
> >
> > > blk_size and blk_count, they are both driver specific, or?
> >
> > Yes, they are driver-specific.  So you cannot use a common upper limit.
>
> And this is why I think my patch has a valid approach. But I am still
> not sure I am getting your point.

My worry here is that if several drivers would do

       .max_blk_count  = UINT_MAX / DRIVER_SPECIFIC_MAX_BLK_SIZE,

Those drivers can safely calculate "max_blk_size * max_blk_count".
People may start assuming this is always safe. while the core cannot do
"GLOBAL_MAX_BLK_SIZE * max_blk_count" using 32-bit arithmetic, as the
latter may still overflow, depending on the driver.

But perhaps I'm just too overcautious...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds



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