Code: static unsigned long ioapic_read_indirect(struct kvm_ioapic *ioapic,
					  unsigned long addr,
					  unsigned long length)
{
	unsigned long result = 0;

	switch (ioapic->ioregsel) {
	case IOAPIC_REG_VERSION:
		result = ((((IOAPIC_NUM_PINS - 1) & 0xff) << 16)
			  | (IOAPIC_VERSION_ID & 0xff));
		break;

	case IOAPIC_REG_APIC_ID:
	case IOAPIC_REG_ARB_ID:
		result = ((ioapic->id & 0xf) << 24);
		break;

	default:
		{
 			u32 redir_index = (ioapic->ioregsel - 0x10) >> 1;
 			u64 redir_content;
 
			ASSERT(redir_index < IOAPIC_NUM_PINS);
 
			redir_content = ioapic->redirtbl[redir_index].bits;
 			result = (ioapic->ioregsel & 0x1) ?
 			    (redir_content >> 32) & 0xffffffff :
 			    redir_content & 0xffffffff;
			break;
		}
	}

	return result;
}

Vulnerability Type: DoS +Info 
CWE ID: CWE-20
Summary: The ioapic_read_indirect function in virt/kvm/ioapic.c in the Linux kernel through 3.8.4 does not properly handle a certain combination of invalid IOAPIC_REG_SELECT and IOAPIC_REG_WINDOW operations, which allows guest OS users to obtain sensitive information from host OS memory or cause a denial of service (host OS OOPS) via a crafted application.
Commit Message: KVM: Fix bounds checking in ioapic indirect register reads (CVE-2013-1798)

If the guest specifies a IOAPIC_REG_SELECT with an invalid value and follows
that with a read of the IOAPIC_REG_WINDOW KVM does not properly validate
that request.  ioapic_read_indirect contains an
ASSERT(redir_index < IOAPIC_NUM_PINS), but the ASSERT has no effect in
non-debug builds.  In recent kernels this allows a guest to cause a kernel
oops by reading invalid memory.  In older kernels (pre-3.3) this allows a
guest to read from large ranges of host memory.

Tested: tested against apic unit tests.

Signed-off-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>