[PATCH][next] clk: imx: pll14xx: Fix potential integer overflow on multiplication
Colin King (gmail)
colin.i.king at gmail.com
Mon Oct 7 03:00:46 PDT 2024
On 07/10/2024 10:54, Dan Carpenter wrote:
> On Mon, Oct 07, 2024 at 09:48:40AM +0100, Colin Ian King wrote:
>> The calculation of fout is using int multiplication and assigning
>> the result to a u64, this can potentially overflow if the int variable
>> mdiv is too large. Fix this by making the 65536 a u64 value to ensure a
>> u64 multiplication is being performed to avoid the overflow.
>>
>> Fixes: 53990cf9d5b4 ("clk: imx: pll14xx: consolidate rate calculation")
>> Signed-off-by: Colin Ian King <colin.i.king at gmail.com>
>
> mdiv is always clamped in then 0-1023 range by one of these:
>
> mdiv = FIELD_GET(MDIV_MASK, pll_div_ctl0);
> mdiv = clamp(mdiv, 64, 1023);
>
> so it can't overflow and the Fixes tag is unnecessary.
Good point.
>
> I think the reason why "fout" is declared as a u64 is because we were worried
> that on 32 bit systems the "fout *=" operation could overflow. That looks
> reasonable to me.
Yes, that makes perfect sense. NAK my patch. Apologies for the noise.
Colin
>
> regards,
> dan carpenter
>
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