[PATCH RFC 3/3] x86/kvm/hyper-v: don't allow to turn on unsupported VMX controls for nested guests

Vitaly Kuznetsov
2020-01-15T17:10:34Z

Sane L1 hypervisors are not supposed to turn any of the unsupported VMX
controls on for its guests and nested_vmx_check_controls() checks for
that. This is, however, not the case for the controls which are supported
on the host but are missing in enlightened VMCS and when eVMCS is in use.

It would certainly be possible to add these missing checks to
nested_check_vm_execution_controls()/_vm_exit_controls()/.. but it seems
preferable to keep eVMCS-specific stuff in eVMCS and reduce the impact on
non-eVMCS guests by doing less unrelated checks. Create a separate
nested_evmcs_check_controls() for this purpose.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/vmx/evmcs.c | 56 ++++++++++++++++++++++++++++++++++++++-
arch/x86/kvm/vmx/evmcs.h | 1 +
arch/x86/kvm/vmx/nested.c | 3 +++
3 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
index b5d6582ba589..88f462866396 100644
--- a/arch/x86/kvm/vmx/evmcs.c
+++ b/arch/x86/kvm/vmx/evmcs.c
@@ -4,9 +4,11 @@
#include <linux/smp.h>

#include "../hyperv.h"
-#include "evmcs.h"
#include "vmcs.h"
+#include "vmcs12.h"
+#include "evmcs.h"
#include "vmx.h"
+#include "trace.h"

DEFINE_STATIC_KEY_FALSE(enable_evmcs);

@@ -378,6 +380,58 @@ void nested_evmcs_filter_control_msr(u32 msr_index, u64 *pdata)
*pdata = ctl_low | ((u64)ctl_high << 32);
}

+int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
+{
+ int ret = 0;
+ u32 unsupp_ctl;
+
+ unsupp_ctl = vmcs12->pin_based_vm_exec_control &
+ EVMCS1_UNSUPPORTED_PINCTRL;
+ if (unsupp_ctl) {
+ trace_kvm_nested_vmenter_failed(
+ "eVMCS: unsupported pin-based VM-execution controls",
+ unsupp_ctl);
+ ret = -EINVAL;
+ }
+
+ unsupp_ctl = vmcs12->secondary_vm_exec_control &
+ EVMCS1_UNSUPPORTED_2NDEXEC;
+ if (unsupp_ctl) {
+ trace_kvm_nested_vmenter_failed(
+ "eVMCS: unsupported secondary VM-execution controls",
+ unsupp_ctl);
+ ret = -EINVAL;
+ }
+
+ unsupp_ctl = vmcs12->vm_exit_controls &
+ EVMCS1_UNSUPPORTED_VMEXIT_CTRL;
+ if (unsupp_ctl) {
+ trace_kvm_nested_vmenter_failed(
+ "eVMCS: unsupported VM-exit controls",
+ unsupp_ctl);
+ ret = -EINVAL;
+ }
+
+ unsupp_ctl = vmcs12->vm_entry_controls &
+ EVMCS1_UNSUPPORTED_VMENTRY_CTRL;
+ if (unsupp_ctl) {
+ trace_kvm_nested_vmenter_failed(
+ "eVMCS: unsupported VM-entry controls",
+ unsupp_ctl);
+ ret = -EINVAL;
+ }
+
+ unsupp_ctl = vmcs12->vm_function_control & EVMCS1_UNSUPPORTED_VMFUNC;
+ if (unsupp_ctl) {
+ trace_kvm_nested_vmenter_failed(
+ "eVMCS: unsupported VM-function controls",
+ unsupp_ctl);
+ ret = -EINVAL;
+ }
+
+ return ret;
+}
+
int nested_enable_evmcs(struct kvm_vcpu *vcpu,
uint16_t *vmcs_version)
{
diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
index b88d9807a796..cb7517a5a41c 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -202,5 +202,6 @@ uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu);
int nested_enable_evmcs(struct kvm_vcpu *vcpu,
uint16_t *vmcs_version);
void nested_evmcs_filter_control_msr(u32 msr_index, u64 *pdata);
+int nested_evmcs_check_controls(struct vmcs12 *vmcs12);

#endif /* __KVM_X86_VMX_EVMCS_H */
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4aea7d304beb..7c720b095663 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2767,6 +2767,9 @@ static int nested_vmx_check_controls(struct kvm_vcpu *vcpu,
nested_check_vm_entry_controls(vcpu, vmcs12))
return -EINVAL;

+ if (to_vmx(vcpu)->nested.enlightened_vmcs_enabled)
+ return nested_evmcs_check_controls(vmcs12);
+
return 0;
}

--
2.24.1