Code: static int load_state_from_tss16(struct x86_emulate_ctxt *ctxt,
				 struct tss_segment_16 *tss)
{
	int ret;
	u8 cpl;

	ctxt->_eip = tss->ip;
	ctxt->eflags = tss->flag | 2;
	*reg_write(ctxt, VCPU_REGS_RAX) = tss->ax;
	*reg_write(ctxt, VCPU_REGS_RCX) = tss->cx;
	*reg_write(ctxt, VCPU_REGS_RDX) = tss->dx;
	*reg_write(ctxt, VCPU_REGS_RBX) = tss->bx;
	*reg_write(ctxt, VCPU_REGS_RSP) = tss->sp;
	*reg_write(ctxt, VCPU_REGS_RBP) = tss->bp;
	*reg_write(ctxt, VCPU_REGS_RSI) = tss->si;
	*reg_write(ctxt, VCPU_REGS_RDI) = tss->di;

	/*
	 * SDM says that segment selectors are loaded before segment
	 * descriptors
	 */
	set_segment_selector(ctxt, tss->ldt, VCPU_SREG_LDTR);
	set_segment_selector(ctxt, tss->es, VCPU_SREG_ES);
	set_segment_selector(ctxt, tss->cs, VCPU_SREG_CS);
	set_segment_selector(ctxt, tss->ss, VCPU_SREG_SS);
	set_segment_selector(ctxt, tss->ds, VCPU_SREG_DS);

	cpl = tss->cs & 3;

	/*
 	 * Now load segment descriptors. If fault happens at this stage
 	 * it is handled in a context of new task
 	 */
	ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl, true);
 	if (ret != X86EMUL_CONTINUE)
 		return ret;
	ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
 	if (ret != X86EMUL_CONTINUE)
 		return ret;
	ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
 	if (ret != X86EMUL_CONTINUE)
 		return ret;
	ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
 	if (ret != X86EMUL_CONTINUE)
 		return ret;
	ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
 	if (ret != X86EMUL_CONTINUE)
 		return ret;
 
	return X86EMUL_CONTINUE;
}

Vulnerability Type: DoS 
CWE ID: CWE-264
Summary: arch/x86/kvm/emulate.c in the KVM subsystem in the Linux kernel through 3.17.2 does not properly perform RIP changes, which allows guest OS users to cause a denial of service (guest OS crash) via a crafted application.
Commit Message: KVM: x86: Handle errors when RIP is set during far jumps

Far jmp/call/ret may fault while loading a new RIP.  Currently KVM does not
handle this case, and may result in failed vm-entry once the assignment is
done.  The tricky part of doing so is that loading the new CS affects the
VMCS/VMCB state, so if we fail during loading the new RIP, we are left in
unconsistent state.  Therefore, this patch saves on 64-bit the old CS
descriptor and restores it if loading RIP failed.

This fixes CVE-2014-3647.

Cc: stable@vger.kernel.org
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>