Re: [BUG] 6.10 stable: arch/x86/kvm/xen.c:1486:44: error: use of uninitialized value ‘port’ [CWE-457]

[Mirsad Todorovac]

On 7/19/24 19:30, Sean Christopherson wrote:
> On Fri, Jul 19, 2024, Mirsad Todorovac wrote:
>> Hi, all,
>>
>> While building stable tree version of 6.10, the following error occurred:
>>
>> In line 1421 defines:
>>
>> 1421        evtchn_port_t port, *ports;
>>
>> The ports becomes &port in line 1470, but neither port nor *ports is assigned a value
>> until line 1486 where port is used:
>>
>> 1485         if (sched_poll.nr_ports == 1)
>> 1486 →               vcpu->arch.xen.poll_evtchn = port;
>>
>> The visual inspection proves that the compiler is again right (GCC 12.3.0).
> 
> Nope, the compiler is wrong.  If sched_poll.nr_ports > 0, then kvm_read_guest_virt()
> will fill ports[sched_poll.nr_ports].  If kvm_read_guest_virt() fails to do so,
> it will return an error and the above code will never be reached.
> 
> 	if (kvm_read_guest_virt(vcpu, (gva_t)sched_poll.ports, ports,
> 				sched_poll.nr_ports * sizeof(*ports), &e)) {
> 		*r = -EFAULT;
> 		return true;
> 	}

Hi again,

I see what you mean.

Apparently, this dependency is not visible by the compiler, and this makes static analysers of
dubious value ...

I might need some advice on how to contribute to the Q/A of the kernel proper and testing suite
...

Best regards,
Mirsad Todorovac