Re: [Qemu-devel] [PATCH 3/3 v2] ppc debug: Add debug stub support

[Alexander Graf]

On 17.06.14 13:05, address@hidden wrote:
> > -----Original Message-----
> > From: Alexander Graf [mailto:address@hidden
> > Sent: Tuesday, June 17, 2014 4:33 PM
> > To: Bhushan Bharat-R65777; address@hidden; address@hidden
> > Subject: Re: [PATCH 3/3 v2] ppc debug: Add debug stub support
> >
> >
> > On 17.06.14 13:01, address@hidden wrote:
> > > > > > > > > +static void kvm_arch_e500_update_guest_debug(CPUState *cs,
> > > > > > > > > +                                             struct
> > > > > > > > > +kvm_guest_debug
> > > > > > > > > +*dbg) {
> > > > > > > > > +    int n;
> > > > > > > > > +
> > > > > > > > > +    if (nb_hw_breakpoint + nb_hw_watchpoint > 0) {
> > > > > > > > > +        dbg->control |= KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_HW_BP;
> > > > > > > > > +        memset(dbg->arch.bp, 0, sizeof(dbg->arch.bp));
> > > > > > > > > +        for (n = 0; n < nb_hw_breakpoint + nb_hw_watchpoint;
> > > > > > > > > + n++) {
> > > > > > > > Boundary check against dbg->arch.bp missing.
> > > > > > > Did not get, what you mean by " dbg->arch.bp missing" ?
> > > > > > dbg->arch.bp is an array of a certain size. If nb_hw_breakpoint +
> > > > > > nb_hw_watchpoint > ARRAY_SIZE(dbg->arch.bp) we might overwrite
> > > > > > memory we don't want to overwrite.
> > > > > Actually this will never overflow here because nb_hw_breakpoint and
> > > > nb_hw_watchpoint overflow in taken care in in hw_insert_breakpoint().
> > > > > Do you thing that to be double safe we can add a check?
> > > > We only check against an overflow of hw_breakpoint[], not dbg->arch.bp.
> > > > What if nb_hw_breakpoint becomes 17?
> > > nb_hw_breakpoint can never be more than max_hw_breakpoint, how
> > nb_hw_breakpoint can be 17 ?
> >
> > Someone comes along and bumps up max_hw_breakpoint to 17?
> You mean some buggy code in qemu does this?

I mean the next person that comes along and touches this code might not 
realize that dbg->arch.bp[] is an array of 16 and by the time I review 
that code I might have forgotten as well :)


Alex