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

[Peter Maydell]

On Thu, 9 Nov 2023 at 15:54, Cédric Le Goater <clg@kaod.org> wrote:
>
> On 11/9/23 16:02, Peter Maydell wrote:
> > 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.
>
> yes. I will add an assert(i2c->num_busses < 64). The current max
> is 16 for POWER10.

We generally make that kind of "property out of range" check
be an error_setg()-and-return, rather than an assert.

thanks
-- PMM