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


From: Peter Maydell
Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH 2/2] hw/arm/smmu-common: Fix coverity issue in get_block_pte_address
Date: Wed, 16 May 2018 16:23:13 +0000

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

thanks
-- PMM



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