Re: [Qemu-devel] [PATCH v4] exec: Fix non-power-of-2 sized accesses

[Paolo Bonzini]

Il 16/08/2013 23:58, Alex Williamson ha scritto:
> Since commit 23326164 we align access sizes to match the alignment of
> the address, but we don't align the access size itself.  This means we
> let illegal access sizes (ex. 3) slip through if the address is
> sufficiently aligned (ex. 4).  This results in an abort which would be
> easy for a guest to trigger.  Account for aligning the access size.

Is it the same as this?

http://lists.gnu.org/archive/html/qemu-devel/2013-07/msg05398.html

(which perhaps is buggy as your v1/v2/v3 :))?

Paolo

> Signed-off-by: Alex Williamson <address@hidden>
> Cc: address@hidden
> ---
> 
> v4: KISS
> v3: Highest power of 2, not lowest
> v2: Remove unnecessary loop condition
> 
>  exec.c |   18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 3ca9381..67a822c 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1924,12 +1924,20 @@ static int memory_access_size(MemoryRegion *mr, 
> unsigned l, hwaddr addr)
>          }
>      }
>  
> -    /* Don't attempt accesses larger than the maximum.  */
> -    if (l > access_size_max) {
> -        l = access_size_max;
> +    /* Don't attempt accesses larger than the maximum or unsupported sizes.  
> */
> +    if (l >= access_size_max) {
> +        return access_size_max;
> +    } else {
> +        if (l >= 8) {
> +            return 8;
> +        } else if (l >= 4) {
> +            return 4;
> +        } else if (l >= 2) {
> +            return 2;
> +        } else {
> +            return 1;
> +        }
>      }
> -
> -    return l;
>  }
>  
>  bool address_space_rw(AddressSpace *as, hwaddr addr, uint8_t *buf,
> 
> 
>