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

[Philippe Mathieu-Daudé]

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)?
Using level_shift() you replaced the trailing 3 by granule_sz. This
means the previous code was only correct for the granule_sz==3 case.

   level_shift(level + 1, granule_sz)
== (granule_sz - 3) * (3 - (level + 1)) + granule_sz;
== (granule_sz - 3) * (4 - level) + granule_sz;
!= (granule_sz - 3) * (4 - level) + 3;

>  
> -    *bsz = 1 << n;
> +    *bsz = 1ULL << n;

For the coverity fix (patch splitted):
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

>      return PTE_ADDRESS(pte, n);
>  }
>  

Regards,

Phil.