kvm: nVMX: Enforce cpl=0 for VMX instructions

From: Felix Wilhelm <fwilhelm@google.com>

VMX instructions executed inside a L1 VM will always trigger a VM exit
even when executed with cpl 3. This means we must perform the
privilege check in software.

Fixes: 70f3aac964ae("kvm: nVMX: Remove superfluous VMX instruction fault checks")
Cc: stable@vger.kernel.org
Signed-off-by: Felix Wilhelm <fwilhelm@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

(cherry picked from commit 727ba748e110b4de50d142edca9d6a9b7e6111d8)
CVE-2018-12904
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 arch/x86/kvm/vmx.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

On 29/06/18 00:31, Tyler Hicks wrote:
> From: Felix Wilhelm <fwilhelm@google.com>
> 
> VMX instructions executed inside a L1 VM will always trigger a VM exit
> even when executed with cpl 3. This means we must perform the
> privilege check in software.
> 
> Fixes: 70f3aac964ae("kvm: nVMX: Remove superfluous VMX instruction fault checks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Felix Wilhelm <fwilhelm@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> (cherry picked from commit 727ba748e110b4de50d142edca9d6a9b7e6111d8)
> CVE-2018-12904
> Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
> ---
>  arch/x86/kvm/vmx.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ddfb9914e105..d81ee9ed4e83 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7402,6 +7402,12 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>  		return 1;
>  	}
>  
> +	/* CPL=0 must be checked manually. */
> +	if (vmx_get_cpl(vcpu)) {
> +		kvm_queue_exception(vcpu, UD_VECTOR);
> +		return 1;
> +	}
> +
>  	if (vmx->nested.vmxon) {
>  		nested_vmx_failValid(vcpu, VMXERR_VMXON_IN_VMX_ROOT_OPERATION);
>  		return kvm_skip_emulated_instruction(vcpu);
> @@ -7461,6 +7467,11 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>   */
>  static int nested_vmx_check_permission(struct kvm_vcpu *vcpu)
>  {
> +	if (vmx_get_cpl(vcpu)) {
> +		kvm_queue_exception(vcpu, UD_VECTOR);
> +		return 0;
> +	}
> +
>  	if (!to_vmx(vcpu)->nested.vmxon) {
>  		kvm_queue_exception(vcpu, UD_VECTOR);
>  		return 0;
> @@ -7794,7 +7805,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu)
>  		if (get_vmx_mem_address(vcpu, exit_qualification,
>  				vmx_instruction_info, true, &gva))
>  			return 1;
> -		/* _system ok, as hardware has verified cpl=0 */
> +		/* _system ok, nested_vmx_check_permission has verified cpl=0 */
>  		kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, gva,
>  			     &field_value, (is_long_mode(vcpu) ? 8 : 4), NULL);
>  	}
> @@ -7937,7 +7948,7 @@ static int handle_vmptrst(struct kvm_vcpu *vcpu)
>  	if (get_vmx_mem_address(vcpu, exit_qualification,
>  			vmx_instruction_info, true, &vmcs_gva))
>  		return 1;
> -	/* ok to use *_system, as hardware has verified cpl=0 */
> +	/* *_system ok, nested_vmx_check_permission has verified cpl=0 */
>  	if (kvm_write_guest_virt_system(&vcpu->arch.emulate_ctxt, vmcs_gva,
>  				 (void *)&to_vmx(vcpu)->nested.current_vmptr,
>  				 sizeof(u64), &e)) {
> 
Clean cherry pick.

Acked-by: Colin Ian King <colin.king@canonical.com>

On Thu, Jun 28, 2018 at 11:31:51PM +0000, Tyler Hicks wrote:
> From: Felix Wilhelm <fwilhelm@google.com>
> 
> VMX instructions executed inside a L1 VM will always trigger a VM exit
> even when executed with cpl 3. This means we must perform the
> privilege check in software.
> 
> Fixes: 70f3aac964ae("kvm: nVMX: Remove superfluous VMX instruction fault checks")
> Cc: stable@vger.kernel.org
> Signed-off-by: Felix Wilhelm <fwilhelm@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> (cherry picked from commit 727ba748e110b4de50d142edca9d6a9b7e6111d8)
> CVE-2018-12904
> Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

Patch looks good.

Acked-by: Seth Forshee <seth.forshee@canonical.com>

Note that unstable already has this commit from the 4.17.2 stable
update.