From: Sean Christopherson sean.j.christopherson@intel.com
commit f958bd2314d117f8c29f4821401bc1925bc2e5ef upstream.
Unlike most state managed by XSAVE, MPX is initialized to zero on INIT. Because INITs are usually recognized in the context of a VCPU_RUN call, kvm_vcpu_reset() puts the guest's FPU so that the FPU state is resident in memory, zeros the MPX state, and reloads FPU state to hardware. But, in the unlikely event that an INIT is recognized during kvm_arch_vcpu_ioctl_get_mpstate() via kvm_apic_accept_events(), kvm_vcpu_reset() will call kvm_put_guest_fpu() without a preceding kvm_load_guest_fpu() and corrupt the guest's FPU state (and possibly userspace's FPU state as well).
Given that MPX is being removed from the kernel[*], fix the bug with the simple-but-ugly approach of loading the guest's FPU during KVM_GET_MP_STATE.
[*] See commit f240652b6032b ("x86/mpx: Remove MPX APIs").
Fixes: f775b13eedee2 ("x86,kvm: move qemu/guest FPU switching out to vcpu_run") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/x86.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8724,6 +8724,8 @@ int kvm_arch_vcpu_ioctl_get_mpstate(stru struct kvm_mp_state *mp_state) { vcpu_load(vcpu); + if (kvm_mpx_supported()) + kvm_load_guest_fpu(vcpu);
kvm_apic_accept_events(vcpu); if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED && @@ -8732,6 +8734,8 @@ int kvm_arch_vcpu_ioctl_get_mpstate(stru else mp_state->mp_state = vcpu->arch.mp_state;
+ if (kvm_mpx_supported()) + kvm_put_guest_fpu(vcpu); vcpu_put(vcpu); return 0; }