Re: [PATCH v2] ppc/pnv: Fix potential overflow in I2C model

[Miles Glenn]

On Thu, 2023-11-09 at 18:15 +0100, Cédric Le Goater 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.
> 
> While we are at it, introduce a PNV_I2C_MAX_BUSSES constant and check
> the number of busses at realize time.
> 
> Fixes: Coverity CID 1523918
> Cc: Glenn Miles <milesg@linux.vnet.ibm.com>
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---
> 
>  v2: - check PNV_I2C_MAX_BUSSES in realize
>      - removed extra space before cast.
> 
>  hw/ppc/pnv_i2c.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/pnv_i2c.c b/hw/ppc/pnv_i2c.c
> index f75e59e70977..483d91d15a77 100644
> --- a/hw/ppc/pnv_i2c.c
> +++ b/hw/ppc/pnv_i2c.c
> @@ -151,6 +151,7 @@
>  #define I2C_RESET_S_SDA_REG             0x11
> 
>  #define PNV_I2C_FIFO_SIZE 8
> +#define PNV_I2C_MAX_BUSSES 64
> 
>  static I2CBus *pnv_i2c_get_bus(PnvI2C *i2c)
>  {
> @@ -437,7 +438,7 @@ 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;
> 
> @@ -641,6 +642,11 @@ static void pnv_i2c_realize(DeviceState *dev,
> Error **errp)
> 
>      assert(i2c->chip);
> 
> +    if (i2c->num_busses > PNV_I2C_MAX_BUSSES) {
> +        error_setg(errp, "Invalid number of busses: %u", i2c-
> >num_busses);
> +        return;
> +    }
> +
>      pnv_xscom_region_init(&i2c->xscom_regs, OBJECT(i2c),
> &pnv_i2c_xscom_ops,
>                            i2c, "xscom-i2c", PNV9_XSCOM_I2CM_SIZE);
> 

Thanks, Cédric.  Looks good to me!

Reviewed-by: Glenn Miles <milesg@linux.vnet.ibm.com>