Re: [Qemu-arm] [Qemu-devel] [PATCH 2/2] hw/arm/smmu-common: Fix coverity issue in get_block_pte_address

[Auger Eric]

Hi Philippe,
On 05/16/2018 10:01 PM, Philippe Mathieu-Daudé wrote:
> On 05/16/2018 01:23 PM, Peter Maydell wrote:
>> On 16 May 2018 at 16:16, Philippe Mathieu-Daudé <address@hidden> wrote:
>>> Hi Eric,
>>>
>>> On 05/16/2018 03:03 PM, Eric Auger wrote:
>>>> Coverity points out that this can overflow if n > 31,
>>>> because it's only doing 32-bit arithmetic. Let's use 1ULL instead
>>>> of 1. Also the formulae used to compute n can be replaced by
>>>> the level_shift() macro.
>>>
>>> This level_shift() replacement doesn't seems that obvious to me, can you
>>> split it in another patch?
>>>
>>>>
>>>> Reported-by: Peter Maydell <address@hidden>
>>>> Signed-off-by: Eric Auger <address@hidden>
>>>> ---
>>>>  hw/arm/smmu-common.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/hw/arm/smmu-common.c b/hw/arm/smmu-common.c
>>>> index 01c7be8..3c5f724 100644
>>>> --- a/hw/arm/smmu-common.c
>>>> +++ b/hw/arm/smmu-common.c
>>>> @@ -83,9 +83,9 @@ static inline hwaddr get_table_pte_address(uint64_t pte, 
>>>> int granule_sz)
>>>>  static inline hwaddr get_block_pte_address(uint64_t pte, int level,
>>>>                                             int granule_sz, uint64_t *bsz)
>>>>  {
>>>> -    int n = (granule_sz - 3) * (4 - level) + 3;
>>>> +    int n = level_shift(level, granule_sz);
>>>
>>> Shouldn't this be level_shift(level + 1, granule_sz)?
>>
>> No. The two expressions are equivalent, they're
>> just arranged differently:
>>
>>    level_shift(lvl, gsz)
>>       == gsz + (3 - lvl) * (gsz - 3)
>>       == gsz + (4 - lvl) * (gsz - 3) - (gsz - 3)
>>       == gsz - gsz + (4 - lvl) * (gsz - 3) + 3
>>       == (gsz - 3) * (4 - lvl) + 3
> 
> Argh I failed this middle school demonstrations...
> 
> Thanks Peter :)
> 
> So for the much cleaner level_shift() use:
> Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

Thank you for the review!

Eric
>