kvm: using uninitialized var in tdp_page_fault

[Sasha Levin]

Hi all,

While fuzzing with syzkaller on the latest -next kernel running on a KVM tools
guest, I've hit the following use of an uninitialized variable:

[  810.783676] UBSAN: Undefined behaviour in arch/x86/kvm/mmu.c:3502:6

[  810.785650] load of value 179 is not a valid value for type '_Bool'

[  810.787554] CPU: 2 PID: 24676 Comm: syz-executor Tainted: G      D         4.4.0-next-20160114-sasha-00021-gf1273d1-dirty #2798

[  810.790792]  1ffff10018213e84 000000008c6fa2f9 ffff8800c109f4a0 ffffffff83433c4e

[  810.792954]  0000000041b58ab3 ffffffff8f960c38 ffffffff83433b86 ffff8800c109f468

[  810.794776]  0000188300000001 000000008c6fa2f9 ffffffff8feb7a20 ffff8800c109f530

[  810.796001] Call Trace:

[  810.796840] dump_stack (lib/dump_stack.c:52)
[  810.798243] ubsan_epilogue (lib/ubsan.c:165)
[  810.802976] __ubsan_handle_load_invalid_value (lib/ubsan.c:454)
[  810.806657] tdp_page_fault (arch/x86/kvm/mmu.c:3502)
[  810.809900] kvm_mmu_page_fault (arch/x86/kvm/mmu.c:4372)
[  810.810517] handle_ept_violation (arch/x86/kvm/vmx.c:5961)
[  810.812386] vmx_handle_exit (arch/x86/kvm/vmx.c:8183)
[  810.817389] vcpu_enter_guest (arch/x86/kvm/x86.c:6677)
[  810.831863] kvm_arch_vcpu_ioctl_run (arch/x86/kvm/x86.c:6741 arch/x86/kvm/x86.c:6894)
[  810.834138] kvm_vcpu_ioctl (arch/x86/kvm/../../../virt/kvm/kvm_main.c:2365)
[  810.840570] do_vfs_ioctl (fs/ioctl.c:44 fs/ioctl.c:674)
[  810.855017] SyS_ioctl (fs/ioctl.c:689 fs/ioctl.c:680)
[  810.856134] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:186)