Re: [Qemu-devel] [PATCH v2] ppc/pnv: check size before data buffer access

[Laurent Vivier <lvivier@redhat.com>]

On 26/10/2018 14:33, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While performing PowerNV memory r/w operations, the access length
> 'sz' could exceed the data[4] buffer size. Add check to avoid OOB
> access.
> 
> Reported-by: Moguofang <moguofang@huawei.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/ppc/pnv_lpc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> Update v2: add error log message
>   -> https://lists.gnu.org/archive/html/qemu-devel/2018-10/msg05750.html
> 
> diff --git a/hw/ppc/pnv_lpc.c b/hw/ppc/pnv_lpc.c
> index d7721320a2..172a915cfc 100644
> --- a/hw/ppc/pnv_lpc.c
> +++ b/hw/ppc/pnv_lpc.c
> @@ -155,9 +155,15 @@ static void pnv_lpc_do_eccb(PnvLpcController *lpc, uint64_t cmd)
>      /* XXX Check for magic bits at the top, addr size etc... */
>      unsigned int sz = (cmd & ECCB_CTL_SZ_MASK) >> ECCB_CTL_SZ_LSH;
>      uint32_t opb_addr = cmd & ECCB_CTL_ADDR_MASK;
> -    uint8_t data[4];
> +    uint8_t data[8];
>      bool success;

I'm not sure 8 is enough.

ECCB_CTL_SZ_MASK is PPC_BITMASK(4, 7), and ECCB_CTL_SZ_LSH is (63 - 7).
So the bitmask is 4 bits wide, and thus sz can be 0 to 15.

I think data[] size should be 16.

Thanks,
Laurent