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

[Cédric Le Goater]

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.

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

yep.

I prefer the cast method than the deposit call. Philippe, I hope you
don't mind ?

Thanks,

C.