Re: [PATCH] ppc/pnv: Fix potential overflow in I2C model

[Peter Maydell]

On Thu, 9 Nov 2023 at 08:06, Cédric Le Goater <clg@kaod.org> wrote:
>
> Coverity warns that "i2c_bus_busy(i2c->busses[i]) << i" might overflow
> because the expression is evaluated using 32-bit arithmetic and then
> used in a context expecting a uint64_t.
>
> Fixes: Coverity CID 1523918
> Cc: Glenn Miles <milesg@linux.vnet.ibm.com>
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---
>  hw/ppc/pnv_i2c.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/ppc/pnv_i2c.c b/hw/ppc/pnv_i2c.c
> index f75e59e70977..ab73c59f7704 100644
> --- a/hw/ppc/pnv_i2c.c
> +++ b/hw/ppc/pnv_i2c.c
> @@ -437,7 +437,7 @@ static uint64_t pnv_i2c_xscom_read(void *opaque, hwaddr 
> addr,
>      case I2C_PORT_BUSY_REG: /* compute busy bit for each port  */
>          val = 0;
>          for (i = 0; i < i2c->num_busses; i++) {
> -            val |= i2c_bus_busy(i2c->busses[i]) << i;
> +            val |= (uint64_t) i2c_bus_busy(i2c->busses[i]) << i;
>          }
>          break;

Should the device's realize function also impose a max
limit on the num-busses property? There doesn't seem to be
anything preventing a caller from setting it to a big
number like 128, which would then be UB here.

Style nit: casts shouldn't have a space after them before
the thing they're casting.

thanks
-- PMM