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

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Message-ID: <ZpqiyxAuobYjkjC-@google.com>
Date: Fri, 19 Jul 2024 10:30:51 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Mirsad Todorovac <mtodorovac69@...il.com>
Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org, 
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [BUG] 6.10 stable: arch/x86/kvm/xen.c:1486:44: error: use of uninitialized value ‘port’ [CWE-457]

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;
	}